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 $217.99   10.559%   $241.0076   $241.01   $241.00   $241.00  
  Purchase #2 $97.80   10.818%   $108.38   $108.38   $108.40   $108.40  
  Purchase #3 $24.72   4.369%   $25.8   $25.80   $25.80   $25.80  
  Purchase #4 $214.28   13.735%   $243.7114   $243.71   $243.70   $243.70  
  Purchase #5 $80.63   13.379%   $91.4175   $91.42   $91.40   $91.40  
  Purchase #6 $26.54   13.393%   $30.0945   $30.09   $30.10   $30.10  
  Purchase #7 $63.83   12.642%   $71.8994   $71.90   $71.90   $71.90  
  7 purchase totals = $725.79       $812.3104   $812.31   $812.30   $812.30