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 $245.64   9.311%   $268.5115   $268.51   $268.50   $268.50  
  Purchase #2 $175.82   10.567%   $194.3989   $194.40   $194.40   $194.40  
  Purchase #3 $164.48   12.640%   $185.2703   $185.27   $185.25   $185.30  
  Purchase #4 $65.49   10.707%   $72.502   $72.50   $72.50   $72.50  
  Purchase #5 $249.70   12.789%   $281.6341   $281.63   $281.65   $281.60  
  Purchase #6 $135.65   10.352%   $149.6925   $149.69   $149.70   $149.70  
  Purchase #7 $45.62   7.328%   $48.963   $48.96   $48.95   $49.00  
  7 purchase totals = $1,082.40       $1,200.9723   $1,200.96   $1,200.95   $1,201.00