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 $228.71   3.533%   $236.7903   $236.79   $236.80   $236.80  
  Purchase #2 $199.27   4.697%   $208.6297   $208.63   $208.65   $208.60  
  Purchase #3 $245.44   4.257%   $255.8884   $255.89   $255.90   $255.90  
  Purchase #4 $56.83   10.812%   $62.9745   $62.97   $62.95   $63.00  
  Purchase #5 $243.62   9.393%   $266.5032   $266.50   $266.50   $266.50  
  Purchase #6 $7.84   13.349%   $8.8866   $8.89   $8.90   $8.90  
  Purchase #7 $13.56   8.651%   $14.7331   $14.73   $14.75   $14.70  
  7 purchase totals = $995.27       $1,054.4058   $1,054.40   $1,054.45   $1,054.40