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 $198.30   8.240%   $214.6399   $214.64   $214.65   $214.60  
  Purchase #2 $5.64   9.194%   $6.1585   $6.16   $6.15   $6.20  
  Purchase #3 $167.90   12.130%   $188.2663   $188.27   $188.25   $188.30  
  Purchase #4 $150.85   8.462%   $163.6149   $163.61   $163.60   $163.60  
  Purchase #5 $30.46   7.408%   $32.7165   $32.72   $32.70   $32.70  
  Purchase #6 $76.82   6.554%   $81.8548   $81.85   $81.85   $81.90  
  Purchase #7 $62.77   8.110%   $67.8606   $67.86   $67.85   $67.90  
  7 purchase totals = $692.74       $755.1115   $755.11   $755.05   $755.20