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 $60.93   12.258%   $68.3988   $68.40   $68.40   $68.40  
  Purchase #2 $52.57   3.165%   $54.2338   $54.23   $54.25   $54.20  
  Purchase #3 $57.87   11.210%   $64.3572   $64.36   $64.35   $64.40  
  Purchase #4 $89.64   3.476%   $92.7559   $92.76   $92.75   $92.80  
  Purchase #5 $209.62   8.704%   $227.8653   $227.87   $227.85   $227.90  
  Purchase #6 $55.84   10.489%   $61.6971   $61.70   $61.70   $61.70  
  Purchase #7 $208.66   8.545%   $226.49   $226.49   $226.50   $226.50  
  7 purchase totals = $735.13       $795.7981   $795.81   $795.80   $795.90