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 $217.90   8.621%   $236.6852   $236.69   $236.70   $236.70  
  Purchase #2 $180.26   12.357%   $202.5347   $202.53   $202.55   $202.50  
  Purchase #3 $230.62   8.686%   $250.6517   $250.65   $250.65   $250.70  
  Purchase #4 $27.76   8.748%   $30.1884   $30.19   $30.20   $30.20  
  Purchase #5 $97.60   5.219%   $102.6937   $102.69   $102.70   $102.70  
  Purchase #6 $149.80   5.873%   $158.5978   $158.60   $158.60   $158.60  
  Purchase #7 $101.28   3.345%   $104.6678   $104.67   $104.65   $104.70  
  7 purchase totals = $1,005.22       $1,086.0193   $1,086.02   $1,086.05   $1,086.10