Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.60   13.852%   $264.8198   $264.82   $264.80   $264.80  
  Purchase #2 $139.42   6.350%   $148.2732   $148.27   $148.25   $148.30  
  Purchase #3 $66.31   4.770%   $69.473   $69.47   $69.45   $69.50  
  Purchase #4 $174.96   11.534%   $195.1399   $195.14   $195.15   $195.10  
  Purchase #5 $199.76   5.343%   $210.4332   $210.43   $210.45   $210.40  
  Purchase #6 $153.83   4.830%   $161.26   $161.26   $161.25   $161.30  
  Purchase #7 $248.47   13.699%   $282.5079   $282.51   $282.50   $282.50  
  7 purchase totals = $1,215.35       $1,331.9070   $1,331.90   $1,331.85   $1,331.90