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 $68.25   7.194%   $73.1599   $73.16   $73.15   $73.20  
  Purchase #2 $195.53   6.741%   $208.7107   $208.71   $208.70   $208.70  
  Purchase #3 $208.68   4.419%   $217.9016   $217.90   $217.90   $217.90  
  Purchase #4 $159.65   12.128%   $179.0124   $179.01   $179.00   $179.00  
  Purchase #5 $40.64   3.234%   $41.9543   $41.95   $41.95   $42.00  
  Purchase #6 $24.85   12.511%   $27.959   $27.96   $27.95   $28.00  
  Purchase #7 $102.99   5.863%   $109.0283   $109.03   $109.05   $109.00  
  7 purchase totals = $800.59       $857.7262   $857.72   $857.70   $857.80