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 $55.90   7.354%   $60.0109   $60.01   $60.00   $60.00  
  Purchase #2 $119.35   12.311%   $134.0432   $134.04   $134.05   $134.00  
  Purchase #3 $12.75   8.216%   $13.7975   $13.80   $13.80   $13.80  
  Purchase #4 $61.88   5.415%   $65.2308   $65.23   $65.25   $65.20  
  Purchase #5 $164.72   5.586%   $173.9213   $173.92   $173.90   $173.90  
  Purchase #6 $169.71   7.248%   $182.0106   $182.01   $182.00   $182.00  
  Purchase #7 $241.61   4.136%   $251.603   $251.60   $251.60   $251.60  
  7 purchase totals = $825.92       $880.6173   $880.61   $880.60   $880.50