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 $72.39   4.409%   $75.5817   $75.58   $75.60   $75.60  
  Purchase #2 $223.69   5.499%   $235.9907   $235.99   $236.00   $236.00  
  Purchase #3 $69.38   8.862%   $75.5285   $75.53   $75.55   $75.50  
  Purchase #4 $114.74   9.267%   $125.373   $125.37   $125.35   $125.40  
  Purchase #5 $85.53   8.336%   $92.6598   $92.66   $92.65   $92.70  
  Purchase #6 $227.73   9.117%   $248.4921   $248.49   $248.50   $248.50  
  Purchase #7 $170.38   5.843%   $180.3353   $180.34   $180.35   $180.30  
  7 purchase totals = $963.84       $1,033.9611   $1,033.96   $1,034.00   $1,034.00