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 $62.26   7.349%   $66.8355   $66.84   $66.85   $66.80  
  Purchase #2 $58.98   7.496%   $63.4011   $63.40   $63.40   $63.40  
  Purchase #3 $88.41   5.117%   $92.9339   $92.93   $92.95   $92.90  
  Purchase #4 $47.89   6.488%   $50.9971   $51.00   $51.00   $51.00  
  Purchase #5 $154.38   5.121%   $162.2858   $162.29   $162.30   $162.30  
  Purchase #6 $44.79   5.697%   $47.3417   $47.34   $47.35   $47.30  
  Purchase #7 $60.96   8.597%   $66.2007   $66.20   $66.20   $66.20  
  7 purchase totals = $517.67       $549.9958   $550.00   $550.05   $549.90