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 $105.25   10.252%   $116.0402   $116.04   $116.05   $116.00  
  Purchase #2 $41.77   8.183%   $45.188   $45.19   $45.20   $45.20  
  Purchase #3 $248.64   7.869%   $268.2055   $268.21   $268.20   $268.20  
  Purchase #4 $29.49   7.197%   $31.6124   $31.61   $31.60   $31.60  
  Purchase #5 $118.85   4.867%   $124.6344   $124.63   $124.65   $124.60  
  Purchase #6 $142.32   4.741%   $149.0674   $149.07   $149.05   $149.10  
  Purchase #7 $249.52   4.738%   $261.3423   $261.34   $261.35   $261.30  
  7 purchase totals = $935.84       $996.0902   $996.09   $996.10   $996.00