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 $61.78   5.262%   $65.0309   $65.03   $65.05   $65.00  
  Purchase #2 $26.47   5.507%   $27.9277   $27.93   $27.95   $27.90  
  Purchase #3 $213.39   5.849%   $225.8712   $225.87   $225.85   $225.90  
  Purchase #4 $237.66   12.842%   $268.1803   $268.18   $268.20   $268.20  
  Purchase #5 $155.74   9.241%   $170.1319   $170.13   $170.15   $170.10  
  Purchase #6 $59.95   5.316%   $63.1369   $63.14   $63.15   $63.10  
  Purchase #7 $137.46   5.367%   $144.8375   $144.84   $144.85   $144.80  
  7 purchase totals = $892.45       $965.1164   $965.12   $965.20   $965.00