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 $37.71   5.346%   $39.726   $39.73   $39.75   $39.70  
  Purchase #2 $76.43   11.658%   $85.3402   $85.34   $85.35   $85.30  
  Purchase #3 $21.60   3.439%   $22.3428   $22.34   $22.35   $22.30  
  Purchase #4 $150.68   12.516%   $169.5391   $169.54   $169.55   $169.50  
  Purchase #5 $164.77   5.568%   $173.9444   $173.94   $173.95   $173.90  
  Purchase #6 $211.61   11.109%   $235.1178   $235.12   $235.10   $235.10  
  Purchase #7 $219.91   4.246%   $229.2474   $229.25   $229.25   $229.20  
  7 purchase totals = $882.71       $955.2577   $955.26   $955.30   $955.00