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 $246.41   3.758%   $255.6701   $255.67   $255.65   $255.70  
  Purchase #2 $97.66   9.519%   $106.9563   $106.96   $106.95   $107.00  
  Purchase #3 $58.64   9.715%   $64.3369   $64.34   $64.35   $64.30  
  Purchase #4 $125.35   11.685%   $139.9971   $140.00   $140.00   $140.00  
  Purchase #5 $244.38   12.760%   $275.5629   $275.56   $275.55   $275.60  
  Purchase #6 $138.90   13.463%   $157.6001   $157.60   $157.60   $157.60  
  Purchase #7 $215.35   5.803%   $227.8468   $227.85   $227.85   $227.80  
  7 purchase totals = $1,126.69       $1,227.9702   $1,227.98   $1,227.95   $1,228.00