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 $58.71   8.659%   $63.7937   $63.79   $63.80   $63.80  
  Purchase #2 $112.61   3.861%   $116.9579   $116.96   $116.95   $117.00  
  Purchase #3 $118.79   7.464%   $127.6565   $127.66   $127.65   $127.70  
  Purchase #4 $32.26   11.604%   $36.0035   $36.00   $36.00   $36.00  
  Purchase #5 $219.63   12.168%   $246.3546   $246.35   $246.35   $246.40  
  Purchase #6 $133.49   3.174%   $137.727   $137.73   $137.75   $137.70  
  Purchase #7 $47.54   12.448%   $53.4578   $53.46   $53.45   $53.50  
  7 purchase totals = $723.03       $781.9510   $781.95   $781.95   $782.10