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 $87.97   7.602%   $94.6575   $94.66   $94.65   $94.70  
  Purchase #2 $21.66   13.742%   $24.6365   $24.64   $24.65   $24.60  
  Purchase #3 $67.38   6.328%   $71.6438   $71.64   $71.65   $71.60  
  Purchase #4 $56.88   7.781%   $61.3058   $61.31   $61.30   $61.30  
  Purchase #5 $139.50   9.479%   $152.7232   $152.72   $152.70   $152.70  
  Purchase #6 $95.46   9.698%   $104.7177   $104.72   $104.70   $104.70  
  Purchase #7 $194.67   3.864%   $202.192   $202.19   $202.20   $202.20  
  7 purchase totals = $663.52       $711.8765   $711.88   $711.85   $711.80