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 $192.95   6.423%   $205.3432   $205.34   $205.35   $205.30  
  Purchase #2 $242.92   5.400%   $256.0377   $256.04   $256.05   $256.00  
  Purchase #3 $115.49   11.461%   $128.7263   $128.73   $128.75   $128.70  
  Purchase #4 $237.30   5.129%   $249.4711   $249.47   $249.45   $249.50  
  Purchase #5 $167.82   10.437%   $185.3354   $185.34   $185.35   $185.30  
  Purchase #6 $144.36   6.265%   $153.4042   $153.40   $153.40   $153.40  
  Purchase #7 $243.80   3.147%   $251.4724   $251.47   $251.45   $251.50  
  7 purchase totals = $1,344.64       $1,429.7903   $1,429.79   $1,429.80   $1,429.70