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 $213.59   9.803%   $234.5282   $234.53   $234.55   $234.50  
  Purchase #2 $200.94   13.605%   $228.2779   $228.28   $228.30   $228.30  
  Purchase #3 $11.86   11.612%   $13.2372   $13.24   $13.25   $13.20  
  Purchase #4 $105.54   9.443%   $115.5061   $115.51   $115.50   $115.50  
  Purchase #5 $22.25   13.467%   $25.2464   $25.25   $25.25   $25.20  
  Purchase #6 $149.27   7.509%   $160.4787   $160.48   $160.50   $160.50  
  Purchase #7 $193.68   10.744%   $214.489   $214.49   $214.50   $214.50  
  7 purchase totals = $897.13       $991.7635   $991.78   $991.85   $991.70