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 $243.86   7.619%   $262.4397   $262.44   $262.45   $262.40  
  Purchase #2 $199.33   11.185%   $221.6251   $221.63   $221.65   $221.60  
  Purchase #3 $109.92   11.852%   $122.9477   $122.95   $122.95   $122.90  
  Purchase #4 $163.89   7.608%   $176.3588   $176.36   $176.35   $176.40  
  Purchase #5 $14.26   8.135%   $15.4201   $15.42   $15.40   $15.40  
  Purchase #6 $238.46   12.400%   $268.029   $268.03   $268.05   $268.00  
  Purchase #7 $135.53   13.455%   $153.7656   $153.77   $153.75   $153.80  
  7 purchase totals = $1,105.25       $1,220.5860   $1,220.60   $1,220.60   $1,220.50