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 $21.31   5.750%   $22.5353   $22.54   $22.55   $22.50  
  Purchase #2 $121.28   4.251%   $126.4356   $126.44   $126.45   $126.40  
  Purchase #3 $75.99   13.483%   $86.2357   $86.24   $86.25   $86.20  
  Purchase #4 $180.29   4.412%   $188.2444   $188.24   $188.25   $188.20  
  Purchase #5 $148.79   7.455%   $159.8823   $159.88   $159.90   $159.90  
  Purchase #6 $42.70   9.614%   $46.8052   $46.81   $46.80   $46.80  
  Purchase #7 $85.78   4.538%   $89.6727   $89.67   $89.65   $89.70  
  7 purchase totals = $676.14       $719.8112   $719.82   $719.85   $719.70