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 $60.33   3.694%   $62.5586   $62.56   $62.55   $62.60  
  Purchase #2 $154.94   6.493%   $165.0003   $165.00   $165.00   $165.00  
  Purchase #3 $182.34   8.302%   $197.4779   $197.48   $197.50   $197.50  
  Purchase #4 $166.76   9.741%   $183.0041   $183.00   $183.00   $183.00  
  Purchase #5 $40.59   5.636%   $42.8777   $42.88   $42.90   $42.90  
  Purchase #6 $63.75   9.568%   $69.8496   $69.85   $69.85   $69.80  
  Purchase #7 $243.45   3.831%   $252.7766   $252.78   $252.80   $252.80  
  7 purchase totals = $912.16       $973.5448   $973.55   $973.60   $973.60