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 $94.71   12.182%   $106.2476   $106.25   $106.25   $106.20  
  Purchase #2 $183.71   12.186%   $206.0969   $206.10   $206.10   $206.10  
  Purchase #3 $209.77   7.189%   $224.8504   $224.85   $224.85   $224.90  
  Purchase #4 $239.89   13.341%   $271.8937   $271.89   $271.90   $271.90  
  Purchase #5 $54.96   13.139%   $62.1812   $62.18   $62.20   $62.20  
  Purchase #6 $52.32   11.644%   $58.4121   $58.41   $58.40   $58.40  
  Purchase #7 $125.56   9.383%   $137.3413   $137.34   $137.35   $137.30  
  7 purchase totals = $960.92       $1,067.0232   $1,067.02   $1,067.05   $1,067.00