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 $214.83   3.512%   $222.3748   $222.37   $222.35   $222.40  
  Purchase #2 $205.33   3.222%   $211.9457   $211.95   $211.95   $211.90  
  Purchase #3 $9.93   4.312%   $10.3582   $10.36   $10.35   $10.40  
  Purchase #4 $166.45   10.294%   $183.5844   $183.58   $183.60   $183.60  
  Purchase #5 $248.73   7.762%   $268.0364   $268.04   $268.05   $268.00  
  Purchase #6 $240.62   11.643%   $268.6354   $268.64   $268.65   $268.60  
  Purchase #7 $75.46   8.151%   $81.6107   $81.61   $81.60   $81.60  
  7 purchase totals = $1,161.35       $1,246.5456   $1,246.55   $1,246.55   $1,246.50