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 $246.46   4.106%   $256.5796   $256.58   $256.60   $256.60  
  Purchase #2 $193.86   4.327%   $202.2483   $202.25   $202.25   $202.20  
  Purchase #3 $155.42   9.232%   $169.7684   $169.77   $169.75   $169.80  
  Purchase #4 $146.74   8.739%   $159.5636   $159.56   $159.55   $159.60  
  Purchase #5 $68.38   5.738%   $72.3036   $72.30   $72.30   $72.30  
  Purchase #6 $206.91   12.138%   $232.0247   $232.02   $232.00   $232.00  
  Purchase #7 $88.63   13.210%   $100.338   $100.34   $100.35   $100.30  
  7 purchase totals = $1,106.40       $1,192.8262   $1,192.82   $1,192.80   $1,192.80