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 $236.92   4.762%   $248.2021   $248.20   $248.20   $248.20  
  Purchase #2 $113.60   3.109%   $117.1318   $117.13   $117.15   $117.10  
  Purchase #3 $133.32   5.166%   $140.2073   $140.21   $140.20   $140.20  
  Purchase #4 $169.70   11.230%   $188.7573   $188.76   $188.75   $188.80  
  Purchase #5 $186.36   10.873%   $206.6229   $206.62   $206.60   $206.60  
  Purchase #6 $248.96   7.225%   $266.9474   $266.95   $266.95   $266.90  
  Purchase #7 $90.94   5.614%   $96.0454   $96.05   $96.05   $96.00  
  7 purchase totals = $1,179.80       $1,263.9142   $1,263.92   $1,263.90   $1,263.80