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 $114.34   4.284%   $119.2383   $119.24   $119.25   $119.20  
  Purchase #2 $64.77   3.405%   $66.9754   $66.98   $67.00   $67.00  
  Purchase #3 $125.51   11.824%   $140.3503   $140.35   $140.35   $140.40  
  Purchase #4 $84.61   8.650%   $91.9288   $91.93   $91.95   $91.90  
  Purchase #5 $98.66   11.498%   $110.0039   $110.00   $110.00   $110.00  
  Purchase #6 $105.54   8.554%   $114.5679   $114.57   $114.55   $114.60  
  Purchase #7 $112.60   12.569%   $126.7527   $126.75   $126.75   $126.80  
  7 purchase totals = $706.03       $769.8173   $769.82   $769.85   $769.90