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 $236.97   9.713%   $259.9869   $259.99   $260.00   $260.00  
  Purchase #2 $196.80   10.293%   $217.0566   $217.06   $217.05   $217.10  
  Purchase #3 $159.46   5.362%   $168.0102   $168.01   $168.00   $168.00  
  Purchase #4 $119.29   3.357%   $123.2946   $123.29   $123.30   $123.30  
  Purchase #5 $153.36   9.168%   $167.42   $167.42   $167.40   $167.40  
  Purchase #6 $55.89   3.554%   $57.8763   $57.88   $57.90   $57.90  
  Purchase #7 $208.84   11.437%   $232.725   $232.73   $232.75   $232.70  
  7 purchase totals = $1,130.61       $1,226.3696   $1,226.38   $1,226.40   $1,226.40