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 $55.88   12.253%   $62.727   $62.73   $62.75   $62.70  
  Purchase #2 $106.33   5.114%   $111.7677   $111.77   $111.75   $111.80  
  Purchase #3 $182.36   8.541%   $197.9354   $197.94   $197.95   $197.90  
  Purchase #4 $67.65   5.434%   $71.3261   $71.33   $71.35   $71.30  
  Purchase #5 $87.67   6.276%   $93.1722   $93.17   $93.15   $93.20  
  Purchase #6 $151.49   4.556%   $158.3919   $158.39   $158.40   $158.40  
  Purchase #7 $20.30   13.412%   $23.0226   $23.02   $23.00   $23.00  
  7 purchase totals = $671.68       $718.3429   $718.35   $718.35   $718.30