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 $221.96   13.649%   $252.2553   $252.26   $252.25   $252.30  
  Purchase #2 $192.27   6.423%   $204.6195   $204.62   $204.60   $204.60  
  Purchase #3 $180.30   3.223%   $186.1111   $186.11   $186.10   $186.10  
  Purchase #4 $161.25   7.618%   $173.534   $173.53   $173.55   $173.50  
  Purchase #5 $96.26   9.807%   $105.7002   $105.70   $105.70   $105.70  
  Purchase #6 $204.80   4.789%   $214.6079   $214.61   $214.60   $214.60  
  Purchase #7 $112.50   12.276%   $126.3105   $126.31   $126.30   $126.30  
  7 purchase totals = $1,169.34       $1,263.1385   $1,263.14   $1,263.10   $1,263.10