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 $175.56   11.403%   $195.5791   $195.58   $195.60   $195.60  
  Purchase #2 $114.84   4.344%   $119.8286   $119.83   $119.85   $119.80  
  Purchase #3 $233.88   6.292%   $248.5957   $248.60   $248.60   $248.60  
  Purchase #4 $132.51   8.614%   $143.9244   $143.92   $143.90   $143.90  
  Purchase #5 $121.38   7.796%   $130.8428   $130.84   $130.85   $130.80  
  Purchase #6 $212.53   12.586%   $239.279   $239.28   $239.30   $239.30  
  Purchase #7 $195.88   5.591%   $206.8317   $206.83   $206.85   $206.80  
  7 purchase totals = $1,186.58       $1,284.8813   $1,284.88   $1,284.95   $1,284.80