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 $54.27   12.314%   $60.9528   $60.95   $60.95   $61.00  
  Purchase #2 $110.94   13.414%   $125.8215   $125.82   $125.80   $125.80  
  Purchase #3 $248.60   12.686%   $280.1374   $280.14   $280.15   $280.10  
  Purchase #4 $84.51   6.500%   $90.0032   $90.00   $90.00   $90.00  
  Purchase #5 $206.77   5.394%   $217.9232   $217.92   $217.90   $217.90  
  Purchase #6 $45.27   7.259%   $48.5561   $48.56   $48.55   $48.60  
  Purchase #7 $129.45   8.427%   $140.3588   $140.36   $140.35   $140.40  
  7 purchase totals = $879.81       $963.7530   $963.75   $963.70   $963.80