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 $95.60   6.621%   $101.9297   $101.93   $101.95   $101.90  
  Purchase #2 $134.50   5.268%   $141.5855   $141.59   $141.60   $141.60  
  Purchase #3 $108.62   13.668%   $123.4662   $123.47   $123.45   $123.50  
  Purchase #4 $64.47   7.242%   $69.1389   $69.14   $69.15   $69.10  
  Purchase #5 $90.26   6.407%   $96.043   $96.04   $96.05   $96.00  
  Purchase #6 $30.54   8.105%   $33.0153   $33.02   $33.00   $33.00  
  Purchase #7 $250.36   6.635%   $266.9714   $266.97   $266.95   $267.00  
  7 purchase totals = $774.35       $832.1500   $832.16   $832.15   $832.10