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 $34.77   6.277%   $36.9525   $36.95   $36.95   $37.00  
  Purchase #2 $200.35   4.548%   $209.4619   $209.46   $209.45   $209.50  
  Purchase #3 $102.81   12.752%   $115.9203   $115.92   $115.90   $115.90  
  Purchase #4 $151.40   8.836%   $164.7777   $164.78   $164.80   $164.80  
  Purchase #5 $247.31   3.289%   $255.444   $255.44   $255.45   $255.40  
  Purchase #6 $27.91   5.828%   $29.5366   $29.54   $29.55   $29.50  
  Purchase #7 $50.30   9.686%   $55.1721   $55.17   $55.15   $55.20  
  7 purchase totals = $814.85       $867.2651   $867.26   $867.25   $867.30