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 $9.75   9.431%   $10.6695   $10.67   $10.65   $10.70  
  Purchase #2 $11.49   9.457%   $12.5766   $12.58   $12.60   $12.60  
  Purchase #3 $239.43   13.261%   $271.1808   $271.18   $271.20   $271.20  
  Purchase #4 $233.38   8.494%   $253.2033   $253.20   $253.20   $253.20  
  Purchase #5 $173.58   8.810%   $188.8724   $188.87   $188.85   $188.90  
  Purchase #6 $235.60   4.377%   $245.9122   $245.91   $245.90   $245.90  
  Purchase #7 $175.66   11.684%   $196.1841   $196.18   $196.20   $196.20  
  7 purchase totals = $1,078.89       $1,178.5989   $1,178.59   $1,178.60   $1,178.70