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 $202.51   12.211%   $227.2385   $227.24   $227.25   $227.20  
  Purchase #2 $101.97   6.205%   $108.2972   $108.30   $108.30   $108.30  
  Purchase #3 $206.43   9.661%   $226.3732   $226.37   $226.35   $226.40  
  Purchase #4 $42.26   12.574%   $47.5738   $47.57   $47.55   $47.60  
  Purchase #5 $162.34   7.831%   $175.0528   $175.05   $175.05   $175.10  
  Purchase #6 $208.47   4.235%   $217.2987   $217.30   $217.30   $217.30  
  Purchase #7 $159.32   10.840%   $176.5903   $176.59   $176.60   $176.60  
  7 purchase totals = $1,083.30       $1,178.4245   $1,178.42   $1,178.40   $1,178.50