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 $148.68   7.157%   $159.321   $159.32   $159.30   $159.30  
  Purchase #2 $71.46   5.546%   $75.4232   $75.42   $75.40   $75.40  
  Purchase #3 $50.47   11.522%   $56.2852   $56.29   $56.30   $56.30  
  Purchase #4 $224.30   3.179%   $231.4305   $231.43   $231.45   $231.40  
  Purchase #5 $135.33   8.446%   $146.76   $146.76   $146.75   $146.80  
  Purchase #6 $59.61   13.712%   $67.7837   $67.78   $67.80   $67.80  
  Purchase #7 $223.79   9.577%   $245.2224   $245.22   $245.20   $245.20  
  7 purchase totals = $913.64       $982.2260   $982.22   $982.20   $982.20