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 $129.65   11.619%   $144.714   $144.71   $144.70   $144.70  
  Purchase #2 $13.98   12.501%   $15.7276   $15.73   $15.75   $15.70  
  Purchase #3 $76.56   6.431%   $81.4836   $81.48   $81.50   $81.50  
  Purchase #4 $87.38   6.648%   $93.189   $93.19   $93.20   $93.20  
  Purchase #5 $26.53   11.534%   $29.59   $29.59   $29.60   $29.60  
  Purchase #6 $43.32   7.140%   $46.413   $46.41   $46.40   $46.40  
  Purchase #7 $42.33   8.531%   $45.9412   $45.94   $45.95   $45.90  
  7 purchase totals = $419.75       $457.0584   $457.05   $457.10   $457.00