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 $211.85   6.807%   $226.2706   $226.27   $226.25   $226.30  
  Purchase #2 $94.82   3.536%   $98.1728   $98.17   $98.15   $98.20  
  Purchase #3 $55.98   5.866%   $59.2638   $59.26   $59.25   $59.30  
  Purchase #4 $250.94   6.773%   $267.9362   $267.94   $267.95   $267.90  
  Purchase #5 $86.37   10.725%   $95.6332   $95.63   $95.65   $95.60  
  Purchase #6 $143.42   3.722%   $148.7581   $148.76   $148.75   $148.80  
  Purchase #7 $26.80   8.834%   $29.1675   $29.17   $29.15   $29.20  
  7 purchase totals = $870.18       $925.2022   $925.20   $925.15   $925.30