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 $136.83   12.511%   $153.9488   $153.95   $153.95   $153.90  
  Purchase #2 $157.60   10.815%   $174.6444   $174.64   $174.65   $174.60  
  Purchase #3 $195.57   3.324%   $202.0707   $202.07   $202.05   $202.10  
  Purchase #4 $111.45   5.634%   $117.7291   $117.73   $117.75   $117.70  
  Purchase #5 $160.83   13.800%   $183.0245   $183.02   $183.00   $183.00  
  Purchase #6 $235.97   10.191%   $260.0177   $260.02   $260.00   $260.00  
  Purchase #7 $163.68   4.863%   $171.6398   $171.64   $171.65   $171.60  
  7 purchase totals = $1,161.93       $1,263.0750   $1,263.07   $1,263.05   $1,262.90