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 $235.87   13.397%   $267.4695   $267.47   $267.45   $267.50  
  Purchase #2 $66.75   8.760%   $72.5973   $72.60   $72.60   $72.60  
  Purchase #3 $192.62   13.326%   $218.2885   $218.29   $218.30   $218.30  
  Purchase #4 $90.47   4.205%   $94.2743   $94.27   $94.25   $94.30  
  Purchase #5 $175.42   6.193%   $186.2838   $186.28   $186.30   $186.30  
  Purchase #6 $137.49   10.565%   $152.0158   $152.02   $152.00   $152.00  
  Purchase #7 $128.83   3.517%   $133.361   $133.36   $133.35   $133.40  
  7 purchase totals = $1,027.45       $1,124.2902   $1,124.29   $1,124.25   $1,124.40