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 $93.88   3.379%   $97.0522   $97.05   $97.05   $97.10  
  Purchase #2 $138.42   9.621%   $151.7374   $151.74   $151.75   $151.70  
  Purchase #3 $249.64   4.370%   $260.5493   $260.55   $260.55   $260.50  
  Purchase #4 $53.88   3.763%   $55.9075   $55.91   $55.90   $55.90  
  Purchase #5 $229.81   5.189%   $241.7348   $241.73   $241.75   $241.70  
  Purchase #6 $158.71   10.537%   $175.4333   $175.43   $175.45   $175.40  
  Purchase #7 $239.92   8.530%   $260.3852   $260.39   $260.40   $260.40  
  7 purchase totals = $1,164.26       $1,242.7997   $1,242.80   $1,242.85   $1,242.70