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 $158.66   10.480%   $175.2876   $175.29   $175.30   $175.30  
  Purchase #2 $59.68   12.690%   $67.2534   $67.25   $67.25   $67.30  
  Purchase #3 $112.39   3.243%   $116.0348   $116.03   $116.05   $116.00  
  Purchase #4 $220.91   3.159%   $227.8885   $227.89   $227.90   $227.90  
  Purchase #5 $105.52   11.278%   $117.4205   $117.42   $117.40   $117.40  
  Purchase #6 $34.91   9.158%   $38.1071   $38.11   $38.10   $38.10  
  Purchase #7 $187.27   8.135%   $202.5044   $202.50   $202.50   $202.50  
  7 purchase totals = $879.34       $944.4963   $944.49   $944.50   $944.50