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 $20.56   9.294%   $22.4708   $22.47   $22.45   $22.50  
  Purchase #2 $40.45   9.361%   $44.2365   $44.24   $44.25   $44.20  
  Purchase #3 $5.75   8.265%   $6.2252   $6.23   $6.25   $6.20  
  Purchase #4 $131.26   12.242%   $147.3288   $147.33   $147.35   $147.30  
  Purchase #5 $76.35   13.601%   $86.7344   $86.73   $86.75   $86.70  
  Purchase #6 $89.45   8.748%   $97.2751   $97.28   $97.30   $97.30  
  Purchase #7 $240.85   7.621%   $259.2052   $259.21   $259.20   $259.20  
  7 purchase totals = $604.67       $663.4760   $663.49   $663.55   $663.40