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 $208.73   7.307%   $223.9819   $223.98   $224.00   $224.00  
  Purchase #2 $244.79   5.564%   $258.4101   $258.41   $258.40   $258.40  
  Purchase #3 $83.36   13.215%   $94.376   $94.38   $94.40   $94.40  
  Purchase #4 $184.64   10.804%   $204.5885   $204.59   $204.60   $204.60  
  Purchase #5 $142.77   10.840%   $158.2463   $158.25   $158.25   $158.20  
  Purchase #6 $85.95   9.506%   $94.1204   $94.12   $94.10   $94.10  
  Purchase #7 $196.69   8.117%   $212.6553   $212.66   $212.65   $212.70  
  7 purchase totals = $1,146.93       $1,246.3785   $1,246.39   $1,246.40   $1,246.40