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 $245.49   5.712%   $259.5124   $259.51   $259.50   $259.50  
  Purchase #2 $169.72   4.443%   $177.2607   $177.26   $177.25   $177.30  
  Purchase #3 $182.38   9.806%   $200.2642   $200.26   $200.25   $200.30  
  Purchase #4 $77.92   10.633%   $86.2052   $86.21   $86.20   $86.20  
  Purchase #5 $110.97   8.111%   $119.9708   $119.97   $119.95   $120.00  
  Purchase #6 $166.40   4.393%   $173.71   $173.71   $173.70   $173.70  
  Purchase #7 $43.86   13.271%   $49.6807   $49.68   $49.70   $49.70  
  7 purchase totals = $996.74       $1,066.6040   $1,066.60   $1,066.55   $1,066.70