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 $193.25   3.234%   $199.4997   $199.50   $199.50   $199.50  
  Purchase #2 $73.83   8.266%   $79.9328   $79.93   $79.95   $79.90  
  Purchase #3 $159.99   13.120%   $180.9807   $180.98   $181.00   $181.00  
  Purchase #4 $49.41   9.635%   $54.1707   $54.17   $54.15   $54.20  
  Purchase #5 $62.27   5.126%   $65.462   $65.46   $65.45   $65.50  
  Purchase #6 $56.82   12.103%   $63.6969   $63.70   $63.70   $63.70  
  Purchase #7 $114.64   3.105%   $118.1996   $118.20   $118.20   $118.20  
  7 purchase totals = $710.21       $761.9424   $761.94   $761.95   $762.00