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 $44.98   3.607%   $46.6024   $46.60   $46.60   $46.60  
  Purchase #2 $245.33   4.405%   $256.1368   $256.14   $256.15   $256.10  
  Purchase #3 $12.79   5.342%   $13.4732   $13.47   $13.45   $13.50  
  Purchase #4 $32.51   12.501%   $36.5741   $36.57   $36.55   $36.60  
  Purchase #5 $125.47   3.141%   $129.411   $129.41   $129.40   $129.40  
  Purchase #6 $185.30   5.382%   $195.2728   $195.27   $195.25   $195.30  
  Purchase #7 $147.96   5.734%   $156.444   $156.44   $156.45   $156.40  
  7 purchase totals = $794.34       $833.9143   $833.90   $833.85   $833.90