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 $244.26   6.154%   $259.2918   $259.29   $259.30   $259.30  
  Purchase #2 $13.74   13.203%   $15.5541   $15.55   $15.55   $15.60  
  Purchase #3 $162.40   8.740%   $176.5938   $176.59   $176.60   $176.60  
  Purchase #4 $172.49   6.370%   $183.4776   $183.48   $183.50   $183.50  
  Purchase #5 $93.58   13.852%   $106.5427   $106.54   $106.55   $106.50  
  Purchase #6 $191.99   11.806%   $214.6563   $214.66   $214.65   $214.70  
  Purchase #7 $241.51   8.608%   $262.2992   $262.30   $262.30   $262.30  
  7 purchase totals = $1,119.97       $1,218.4155   $1,218.41   $1,218.45   $1,218.50