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 $91.86   6.452%   $97.7868   $97.79   $97.80   $97.80  
  Purchase #2 $161.44   13.201%   $182.7517   $182.75   $182.75   $182.80  
  Purchase #3 $207.41   4.383%   $216.5008   $216.50   $216.50   $216.50  
  Purchase #4 $214.58   9.407%   $234.7655   $234.77   $234.75   $234.80  
  Purchase #5 $93.74   4.704%   $98.1495   $98.15   $98.15   $98.10  
  Purchase #6 $224.57   9.814%   $246.6093   $246.61   $246.60   $246.60  
  Purchase #7 $218.60   8.336%   $236.8225   $236.82   $236.80   $236.80  
  7 purchase totals = $1,212.20       $1,313.3861   $1,313.39   $1,313.35   $1,313.40