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 $62.54   6.472%   $66.5876   $66.59   $66.60   $66.60  
  Purchase #2 $130.28   9.266%   $142.3517   $142.35   $142.35   $142.40  
  Purchase #3 $110.64   4.464%   $115.579   $115.58   $115.60   $115.60  
  Purchase #4 $103.53   11.450%   $115.3842   $115.38   $115.40   $115.40  
  Purchase #5 $215.70   6.156%   $228.9785   $228.98   $229.00   $229.00  
  Purchase #6 $19.55   3.642%   $20.262   $20.26   $20.25   $20.30  
  Purchase #7 $128.96   6.161%   $136.9052   $136.91   $136.90   $136.90  
  7 purchase totals = $771.20       $826.0482   $826.05   $826.10   $826.20