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 $218.67   13.706%   $248.6409   $248.64   $248.65   $248.60  
  Purchase #2 $135.89   9.647%   $148.9993   $149.00   $149.00   $149.00  
  Purchase #3 $176.89   10.225%   $194.977   $194.98   $195.00   $195.00  
  Purchase #4 $192.67   3.545%   $199.5002   $199.50   $199.50   $199.50  
  Purchase #5 $97.40   10.483%   $107.6104   $107.61   $107.60   $107.60  
  Purchase #6 $169.73   9.123%   $185.2145   $185.21   $185.20   $185.20  
  Purchase #7 $203.27   12.240%   $228.1502   $228.15   $228.15   $228.20  
  7 purchase totals = $1,194.52       $1,313.0925   $1,313.09   $1,313.10   $1,313.10