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 $65.82   7.847%   $70.9849   $70.98   $71.00   $71.00  
  Purchase #2 $107.92   10.594%   $119.353   $119.35   $119.35   $119.40  
  Purchase #3 $96.35   5.734%   $101.8747   $101.87   $101.85   $101.90  
  Purchase #4 $79.58   7.382%   $85.4546   $85.45   $85.45   $85.50  
  Purchase #5 $242.38   6.705%   $258.6316   $258.63   $258.65   $258.60  
  Purchase #6 $22.41   13.236%   $25.3762   $25.38   $25.40   $25.40  
  Purchase #7 $237.55   13.764%   $270.2464   $270.25   $270.25   $270.20  
  7 purchase totals = $852.01       $931.9214   $931.91   $931.95   $932.00