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 $118.95   8.449%   $129.0001   $129.00   $129.00   $129.00  
  Purchase #2 $123.89   6.810%   $132.3269   $132.33   $132.35   $132.30  
  Purchase #3 $14.35   7.114%   $15.3709   $15.37   $15.35   $15.40  
  Purchase #4 $32.61   4.491%   $34.0745   $34.07   $34.05   $34.10  
  Purchase #5 $83.54   10.278%   $92.1262   $92.13   $92.15   $92.10  
  Purchase #6 $213.90   9.393%   $233.9916   $233.99   $234.00   $234.00  
  Purchase #7 $80.63   8.617%   $87.5779   $87.58   $87.60   $87.60  
  7 purchase totals = $667.87       $724.4681   $724.47   $724.50   $724.50