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 $218.40   13.647%   $248.205   $248.21   $248.20   $248.20  
  Purchase #2 $237.29   8.172%   $256.6813   $256.68   $256.70   $256.70  
  Purchase #3 $25.34   8.486%   $27.4904   $27.49   $27.50   $27.50  
  Purchase #4 $247.95   6.367%   $263.737   $263.74   $263.75   $263.70  
  Purchase #5 $80.74   3.566%   $83.6192   $83.62   $83.60   $83.60  
  Purchase #6 $38.74   7.327%   $41.5785   $41.58   $41.60   $41.60  
  Purchase #7 $173.43   6.640%   $184.9458   $184.95   $184.95   $184.90  
  7 purchase totals = $1,021.89       $1,106.2572   $1,106.27   $1,106.30   $1,106.20