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 $93.80   3.106%   $96.7134   $96.71   $96.70   $96.70  
  Purchase #2 $238.43   4.772%   $249.8079   $249.81   $249.80   $249.80  
  Purchase #3 $241.39   5.286%   $254.1499   $254.15   $254.15   $254.10  
  Purchase #4 $245.34   8.162%   $265.3647   $265.36   $265.35   $265.40  
  Purchase #5 $50.36   12.733%   $56.7723   $56.77   $56.75   $56.80  
  Purchase #6 $238.50   6.386%   $253.7306   $253.73   $253.75   $253.70  
  Purchase #7 $214.53   5.476%   $226.2777   $226.28   $226.30   $226.30  
  7 purchase totals = $1,322.35       $1,402.8165   $1,402.81   $1,402.80   $1,402.80