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 $41.61   7.259%   $44.6305   $44.63   $44.65   $44.60  
  Purchase #2 $114.44   12.870%   $129.1684   $129.17   $129.15   $129.20  
  Purchase #3 $44.93   13.750%   $51.1079   $51.11   $51.10   $51.10  
  Purchase #4 $86.25   8.195%   $93.3182   $93.32   $93.30   $93.30  
  Purchase #5 $119.39   11.268%   $132.8429   $132.84   $132.85   $132.80  
  Purchase #6 $74.37   5.182%   $78.2239   $78.22   $78.20   $78.20  
  Purchase #7 $187.94   3.540%   $194.5931   $194.59   $194.60   $194.60  
  7 purchase totals = $668.93       $723.8849   $723.88   $723.85   $723.80