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 $58.32   13.556%   $66.2259   $66.23   $66.25   $66.20  
  Purchase #2 $136.77   3.628%   $141.732   $141.73   $141.75   $141.70  
  Purchase #3 $218.79   13.147%   $247.5543   $247.55   $247.55   $247.60  
  Purchase #4 $153.54   9.226%   $167.7056   $167.71   $167.70   $167.70  
  Purchase #5 $27.28   4.684%   $28.5578   $28.56   $28.55   $28.60  
  Purchase #6 $11.52   7.541%   $12.3887   $12.39   $12.40   $12.40  
  Purchase #7 $151.63   5.383%   $159.7922   $159.79   $159.80   $159.80  
  7 purchase totals = $757.85       $823.9565   $823.96   $824.00   $824.00