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 $245.96   8.540%   $266.965   $266.97   $266.95   $267.00  
  Purchase #2 $38.79   3.754%   $40.2462   $40.25   $40.25   $40.20  
  Purchase #3 $235.38   7.491%   $253.0123   $253.01   $253.00   $253.00  
  Purchase #4 $206.63   13.202%   $233.9093   $233.91   $233.90   $233.90  
  Purchase #5 $120.44   4.262%   $125.5732   $125.57   $125.55   $125.60  
  Purchase #6 $166.46   8.750%   $181.0253   $181.03   $181.05   $181.00  
  Purchase #7 $185.27   10.665%   $205.029   $205.03   $205.05   $205.00  
  7 purchase totals = $1,198.93       $1,305.7603   $1,305.77   $1,305.75   $1,305.70