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 $233.63   11.800%   $261.1983   $261.20   $261.20   $261.20  
  Purchase #2 $179.63   13.148%   $203.2478   $203.25   $203.25   $203.20  
  Purchase #3 $48.40   7.347%   $51.9559   $51.96   $51.95   $52.00  
  Purchase #4 $7.37   11.716%   $8.2335   $8.23   $8.25   $8.20  
  Purchase #5 $249.32   6.771%   $266.2015   $266.20   $266.20   $266.20  
  Purchase #6 $24.73   3.516%   $25.5995   $25.60   $25.60   $25.60  
  Purchase #7 $180.98   13.447%   $205.3164   $205.32   $205.30   $205.30  
  7 purchase totals = $924.06       $1,021.7529   $1,021.76   $1,021.75   $1,021.70