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 $237.93   12.189%   $266.9313   $266.93   $266.95   $266.90  
  Purchase #2 $45.54   12.452%   $51.2106   $51.21   $51.20   $51.20  
  Purchase #3 $127.25   3.709%   $131.9697   $131.97   $131.95   $132.00  
  Purchase #4 $62.57   6.190%   $66.4431   $66.44   $66.45   $66.40  
  Purchase #5 $56.35   6.731%   $60.1429   $60.14   $60.15   $60.10  
  Purchase #6 $155.45   10.411%   $171.6339   $171.63   $171.65   $171.60  
  Purchase #7 $200.30   8.321%   $216.967   $216.97   $216.95   $217.00  
  7 purchase totals = $885.39       $965.2985   $965.29   $965.30   $965.20