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 $119.69   11.632%   $133.6123   $133.61   $133.60   $133.60  
  Purchase #2 $237.67   6.566%   $253.2754   $253.28   $253.30   $253.30  
  Purchase #3 $115.77   5.343%   $121.9556   $121.96   $121.95   $122.00  
  Purchase #4 $240.28   11.392%   $267.6527   $267.65   $267.65   $267.70  
  Purchase #5 $172.29   5.646%   $182.0175   $182.02   $182.00   $182.00  
  Purchase #6 $17.33   3.553%   $17.9457   $17.95   $17.95   $17.90  
  Purchase #7 $233.38   3.601%   $241.784   $241.78   $241.80   $241.80  
  7 purchase totals = $1,136.41       $1,218.2432   $1,218.25   $1,218.25   $1,218.30