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 $42.41   13.541%   $48.1527   $48.15   $48.15   $48.20  
  Purchase #2 $157.61   12.171%   $176.7927   $176.79   $176.80   $176.80  
  Purchase #3 $186.92   12.328%   $209.9635   $209.96   $209.95   $210.00  
  Purchase #4 $215.49   12.418%   $242.2495   $242.25   $242.25   $242.20  
  Purchase #5 $64.42   5.339%   $67.8594   $67.86   $67.85   $67.90  
  Purchase #6 $67.49   12.555%   $75.9634   $75.96   $75.95   $76.00  
  Purchase #7 $207.97   8.395%   $225.4291   $225.43   $225.45   $225.40  
  7 purchase totals = $942.31       $1,046.4103   $1,046.40   $1,046.40   $1,046.50