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 $195.72   5.620%   $206.7195   $206.72   $206.70   $206.70  
  Purchase #2 $168.85   11.308%   $187.9436   $187.94   $187.95   $187.90  
  Purchase #3 $215.40   8.543%   $233.8016   $233.80   $233.80   $233.80  
  Purchase #4 $102.40   5.637%   $108.1723   $108.17   $108.15   $108.20  
  Purchase #5 $245.75   4.751%   $257.4256   $257.43   $257.45   $257.40  
  Purchase #6 $153.78   6.756%   $164.1694   $164.17   $164.15   $164.20  
  Purchase #7 $168.47   5.742%   $178.1435   $178.14   $178.15   $178.10  
  7 purchase totals = $1,250.37       $1,336.3755   $1,336.37   $1,336.35   $1,336.30