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 $66.79   5.520%   $70.4768   $70.48   $70.50   $70.50  
  Purchase #2 $176.37   5.237%   $185.6065   $185.61   $185.60   $185.60  
  Purchase #3 $14.40   9.458%   $15.762   $15.76   $15.75   $15.80  
  Purchase #4 $192.31   5.788%   $203.4409   $203.44   $203.45   $203.40  
  Purchase #5 $118.98   12.239%   $133.542   $133.54   $133.55   $133.50  
  Purchase #6 $61.67   8.474%   $66.8959   $66.90   $66.90   $66.90  
  Purchase #7 $22.92   10.236%   $25.2661   $25.27   $25.25   $25.30  
  7 purchase totals = $653.44       $700.9902   $701.00   $701.00   $701.00