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 $192.48   8.172%   $208.2095   $208.21   $208.20   $208.20  
  Purchase #2 $176.91   7.774%   $190.663   $190.66   $190.65   $190.70  
  Purchase #3 $56.54   6.382%   $60.1484   $60.15   $60.15   $60.10  
  Purchase #4 $76.59   10.759%   $84.8303   $84.83   $84.85   $84.80  
  Purchase #5 $53.51   6.373%   $56.9202   $56.92   $56.90   $56.90  
  Purchase #6 $193.97   11.813%   $216.8837   $216.88   $216.90   $216.90  
  Purchase #7 $123.86   5.458%   $130.6203   $130.62   $130.60   $130.60  
  7 purchase totals = $873.86       $948.2754   $948.27   $948.25   $948.20