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 $88.57   8.713%   $96.2871   $96.29   $96.30   $96.30  
  Purchase #2 $146.36   6.820%   $156.3418   $156.34   $156.35   $156.30  
  Purchase #3 $151.70   7.867%   $163.6342   $163.63   $163.65   $163.60  
  Purchase #4 $116.61   13.587%   $132.4538   $132.45   $132.45   $132.50  
  Purchase #5 $242.54   11.820%   $271.2082   $271.21   $271.20   $271.20  
  Purchase #6 $164.47   5.318%   $173.2165   $173.22   $173.20   $173.20  
  Purchase #7 $47.74   8.309%   $51.7067   $51.71   $51.70   $51.70  
  7 purchase totals = $957.99       $1,044.8483   $1,044.85   $1,044.85   $1,044.80