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 $168.51   10.501%   $186.2052   $186.21   $186.20   $186.20  
  Purchase #2 $185.29   12.437%   $208.3345   $208.33   $208.35   $208.30  
  Purchase #3 $116.26   3.128%   $119.8966   $119.90   $119.90   $119.90  
  Purchase #4 $229.32   6.691%   $244.6638   $244.66   $244.65   $244.70  
  Purchase #5 $29.79   6.684%   $31.7812   $31.78   $31.80   $31.80  
  Purchase #6 $136.89   8.716%   $148.8213   $148.82   $148.80   $148.80  
  Purchase #7 $62.46   9.772%   $68.5636   $68.56   $68.55   $68.60  
  7 purchase totals = $928.52       $1,008.2662   $1,008.26   $1,008.25   $1,008.30