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 $114.79   11.496%   $127.9863   $127.99   $128.00   $128.00  
  Purchase #2 $205.87   4.585%   $215.3091   $215.31   $215.30   $215.30  
  Purchase #3 $70.55   5.211%   $74.2264   $74.23   $74.25   $74.20  
  Purchase #4 $81.74   13.447%   $92.7316   $92.73   $92.75   $92.70  
  Purchase #5 $152.88   9.599%   $167.555   $167.56   $167.55   $167.60  
  Purchase #6 $57.61   11.708%   $64.355   $64.36   $64.35   $64.40  
  Purchase #7 $195.88   13.132%   $221.603   $221.60   $221.60   $221.60  
  7 purchase totals = $879.32       $963.7664   $963.78   $963.80   $963.80