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 $118.98   4.832%   $124.7291   $124.73   $124.75   $124.70  
  Purchase #2 $92.95   9.429%   $101.7143   $101.71   $101.70   $101.70  
  Purchase #3 $82.44   11.702%   $92.0871   $92.09   $92.10   $92.10  
  Purchase #4 $237.30   11.813%   $265.3322   $265.33   $265.35   $265.30  
  Purchase #5 $72.30   3.487%   $74.8211   $74.82   $74.80   $74.80  
  Purchase #6 $65.55   13.782%   $74.5841   $74.58   $74.60   $74.60  
  Purchase #7 $176.99   5.252%   $186.2855   $186.29   $186.30   $186.30  
  7 purchase totals = $846.51       $919.5534   $919.55   $919.60   $919.50