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 $204.95   7.117%   $219.5363   $219.54   $219.55   $219.50  
  Purchase #2 $74.55   3.357%   $77.0526   $77.05   $77.05   $77.10  
  Purchase #3 $24.64   5.532%   $26.0031   $26.00   $26.00   $26.00  
  Purchase #4 $41.44   13.306%   $46.954   $46.95   $46.95   $47.00  
  Purchase #5 $12.69   6.363%   $13.4975   $13.50   $13.50   $13.50  
  Purchase #6 $223.60   4.741%   $234.2009   $234.20   $234.20   $234.20  
  Purchase #7 $204.92   13.281%   $232.1354   $232.14   $232.15   $232.10  
  7 purchase totals = $786.79       $849.3798   $849.38   $849.40   $849.40