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 $244.87   8.236%   $265.0375   $265.04   $265.05   $265.00  
  Purchase #2 $216.98   10.318%   $239.368   $239.37   $239.35   $239.40  
  Purchase #3 $76.73   10.707%   $84.9455   $84.95   $84.95   $84.90  
  Purchase #4 $96.96   8.541%   $105.2414   $105.24   $105.25   $105.20  
  Purchase #5 $223.35   12.174%   $250.5406   $250.54   $250.55   $250.50  
  Purchase #6 $38.71   8.860%   $42.1397   $42.14   $42.15   $42.10  
  Purchase #7 $168.43   9.337%   $184.1563   $184.16   $184.15   $184.20  
  7 purchase totals = $1,066.03       $1,171.4290   $1,171.44   $1,171.45   $1,171.30