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 $62.42   7.262%   $66.9529   $66.95   $66.95   $67.00  
  Purchase #2 $16.96   9.703%   $18.6056   $18.61   $18.60   $18.60  
  Purchase #3 $60.60   11.763%   $67.7284   $67.73   $67.75   $67.70  
  Purchase #4 $191.84   10.840%   $212.6355   $212.64   $212.65   $212.60  
  Purchase #5 $94.42   13.776%   $107.4273   $107.43   $107.45   $107.40  
  Purchase #6 $47.73   5.198%   $50.211   $50.21   $50.20   $50.20  
  Purchase #7 $64.34   8.355%   $69.7156   $69.72   $69.70   $69.70  
  7 purchase totals = $538.31       $593.2763   $593.29   $593.30   $593.20