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 $227.27   6.398%   $241.8107   $241.81   $241.80   $241.80  
  Purchase #2 $10.78   3.825%   $11.1923   $11.19   $11.20   $11.20  
  Purchase #3 $62.87   6.842%   $67.1716   $67.17   $67.15   $67.20  
  Purchase #4 $161.67   9.477%   $176.9915   $176.99   $177.00   $177.00  
  Purchase #5 $71.42   6.615%   $76.1444   $76.14   $76.15   $76.10  
  Purchase #6 $116.34   7.461%   $125.0201   $125.02   $125.00   $125.00  
  Purchase #7 $23.84   11.164%   $26.5015   $26.50   $26.50   $26.50  
  7 purchase totals = $674.19       $724.8321   $724.82   $724.80   $724.80