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 $217.71   10.506%   $240.5826   $240.58   $240.60   $240.60  
  Purchase #2 $176.47   11.598%   $196.937   $196.94   $196.95   $196.90  
  Purchase #3 $11.33   4.137%   $11.7987   $11.80   $11.80   $11.80  
  Purchase #4 $24.91   5.212%   $26.2083   $26.21   $26.20   $26.20  
  Purchase #5 $187.84   8.754%   $204.2835   $204.28   $204.30   $204.30  
  Purchase #6 $47.47   13.477%   $53.8675   $53.87   $53.85   $53.90  
  Purchase #7 $185.54   3.831%   $192.648   $192.65   $192.65   $192.60  
  7 purchase totals = $851.27       $926.3256   $926.33   $926.35   $926.30