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 $217.79   8.344%   $235.9624   $235.96   $235.95   $236.00  
  Purchase #2 $30.56   11.746%   $34.1496   $34.15   $34.15   $34.10  
  Purchase #3 $246.64   9.262%   $269.4838   $269.48   $269.50   $269.50  
  Purchase #4 $238.63   11.827%   $266.8528   $266.85   $266.85   $266.90  
  Purchase #5 $129.29   13.418%   $146.6381   $146.64   $146.65   $146.60  
  Purchase #6 $62.25   3.492%   $64.4238   $64.42   $64.40   $64.40  
  Purchase #7 $157.41   13.329%   $178.3912   $178.39   $178.40   $178.40  
  7 purchase totals = $1,082.57       $1,195.9017   $1,195.89   $1,195.90   $1,195.90