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 $204.73   10.548%   $226.3249   $226.32   $226.30   $226.30  
  Purchase #2 $118.76   11.674%   $132.624   $132.62   $132.60   $132.60  
  Purchase #3 $22.67   12.854%   $25.584   $25.58   $25.60   $25.60  
  Purchase #4 $47.68   9.549%   $52.233   $52.23   $52.25   $52.20  
  Purchase #5 $11.39   10.287%   $12.5617   $12.56   $12.55   $12.60  
  Purchase #6 $230.29   5.371%   $242.6589   $242.66   $242.65   $242.70  
  Purchase #7 $234.29   6.671%   $249.9195   $249.92   $249.90   $249.90  
  7 purchase totals = $869.81       $941.9060   $941.89   $941.85   $941.90