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 $41.51   13.846%   $47.2575   $47.26   $47.25   $47.30  
  Purchase #2 $147.43   7.417%   $158.3649   $158.36   $158.35   $158.40  
  Purchase #3 $209.77   10.542%   $231.884   $231.88   $231.90   $231.90  
  Purchase #4 $130.45   4.523%   $136.3503   $136.35   $136.35   $136.40  
  Purchase #5 $164.50   11.483%   $183.3895   $183.39   $183.40   $183.40  
  Purchase #6 $107.69   12.868%   $121.5475   $121.55   $121.55   $121.50  
  Purchase #7 $141.47   9.539%   $154.9648   $154.96   $154.95   $155.00  
  7 purchase totals = $942.82       $1,033.7585   $1,033.75   $1,033.75   $1,033.90