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 $74.69   11.478%   $83.2629   $83.26   $83.25   $83.30  
  Purchase #2 $185.51   10.436%   $204.8698   $204.87   $204.85   $204.90  
  Purchase #3 $82.75   4.181%   $86.2098   $86.21   $86.20   $86.20  
  Purchase #4 $61.57   8.569%   $66.8459   $66.85   $66.85   $66.80  
  Purchase #5 $186.67   11.748%   $208.6   $208.60   $208.60   $208.60  
  Purchase #6 $185.39   8.129%   $200.4604   $200.46   $200.45   $200.50  
  Purchase #7 $222.29   5.291%   $234.0514   $234.05   $234.05   $234.10  
  7 purchase totals = $998.87       $1,084.3002   $1,084.30   $1,084.25   $1,084.40