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 $72.91   3.538%   $75.4896   $75.49   $75.50   $75.50  
  Purchase #2 $119.39   5.376%   $125.8084   $125.81   $125.80   $125.80  
  Purchase #3 $116.32   10.189%   $128.1718   $128.17   $128.15   $128.20  
  Purchase #4 $30.67   11.130%   $34.0836   $34.08   $34.10   $34.10  
  Purchase #5 $186.73   4.842%   $195.7715   $195.77   $195.75   $195.80  
  Purchase #6 $113.50   3.630%   $117.6201   $117.62   $117.60   $117.60  
  Purchase #7 $100.79   4.840%   $105.6682   $105.67   $105.65   $105.70  
  7 purchase totals = $740.31       $782.6132   $782.61   $782.55   $782.70