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 $250.62   6.657%   $267.3038   $267.30   $267.30   $267.30  
  Purchase #2 $214.57   10.666%   $237.456   $237.46   $237.45   $237.50  
  Purchase #3 $41.82   10.462%   $46.1952   $46.20   $46.20   $46.20  
  Purchase #4 $93.94   10.330%   $103.644   $103.64   $103.65   $103.60  
  Purchase #5 $16.71   8.845%   $18.188   $18.19   $18.20   $18.20  
  Purchase #6 $92.58   11.679%   $103.3924   $103.39   $103.40   $103.40  
  Purchase #7 $43.56   10.821%   $48.2736   $48.27   $48.25   $48.30  
  7 purchase totals = $753.80       $824.4530   $824.45   $824.45   $824.50