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 $199.89   12.373%   $224.6224   $224.62   $224.60   $224.60  
  Purchase #2 $177.67   4.388%   $185.4662   $185.47   $185.45   $185.50  
  Purchase #3 $35.82   7.633%   $38.5541   $38.55   $38.55   $38.60  
  Purchase #4 $89.31   10.734%   $98.8965   $98.90   $98.90   $98.90  
  Purchase #5 $22.82   9.257%   $24.9324   $24.93   $24.95   $24.90  
  Purchase #6 $189.53   9.762%   $208.0319   $208.03   $208.05   $208.00  
  Purchase #7 $241.90   4.286%   $252.2678   $252.27   $252.25   $252.30  
  7 purchase totals = $956.94       $1,032.7713   $1,032.77   $1,032.75   $1,032.80