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 $14.46   5.403%   $15.2413   $15.24   $15.25   $15.20  
  Purchase #2 $58.73   10.495%   $64.8937   $64.89   $64.90   $64.90  
  Purchase #3 $110.33   13.431%   $125.1484   $125.15   $125.15   $125.10  
  Purchase #4 $173.63   4.387%   $181.2471   $181.25   $181.25   $181.20  
  Purchase #5 $73.25   8.449%   $79.4389   $79.44   $79.45   $79.40  
  Purchase #6 $180.63   6.467%   $192.3113   $192.31   $192.30   $192.30  
  Purchase #7 $244.92   8.704%   $266.2378   $266.24   $266.25   $266.20  
  7 purchase totals = $855.95       $924.5185   $924.52   $924.55   $924.30