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 $247.79   5.596%   $261.6563   $261.66   $261.65   $261.70  
  Purchase #2 $18.60   4.638%   $19.4627   $19.46   $19.45   $19.50  
  Purchase #3 $46.35   5.697%   $48.9906   $48.99   $49.00   $49.00  
  Purchase #4 $176.86   11.705%   $197.5615   $197.56   $197.55   $197.60  
  Purchase #5 $65.93   4.246%   $68.7294   $68.73   $68.75   $68.70  
  Purchase #6 $237.70   8.628%   $258.2088   $258.21   $258.20   $258.20  
  Purchase #7 $203.38   7.861%   $219.3677   $219.37   $219.35   $219.40  
  7 purchase totals = $996.61       $1,073.9770   $1,073.98   $1,073.95   $1,074.10