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 $78.95   10.245%   $87.0384   $87.04   $87.05   $87.00  
  Purchase #2 $33.62   4.873%   $35.2583   $35.26   $35.25   $35.30  
  Purchase #3 $200.47   3.627%   $207.741   $207.74   $207.75   $207.70  
  Purchase #4 $88.99   7.307%   $95.4925   $95.49   $95.50   $95.50  
  Purchase #5 $73.89   3.204%   $76.2574   $76.26   $76.25   $76.30  
  Purchase #6 $136.59   5.717%   $144.3989   $144.40   $144.40   $144.40  
  Purchase #7 $146.62   8.282%   $158.7631   $158.76   $158.75   $158.80  
  7 purchase totals = $759.13       $804.9496   $804.95   $804.95   $805.00