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 $61.81   7.183%   $66.2498   $66.25   $66.25   $66.20  
  Purchase #2 $96.60   10.710%   $106.9459   $106.95   $106.95   $106.90  
  Purchase #3 $169.94   3.814%   $176.4215   $176.42   $176.40   $176.40  
  Purchase #4 $158.64   9.618%   $173.898   $173.90   $173.90   $173.90  
  Purchase #5 $5.63   8.431%   $6.1047   $6.10   $6.10   $6.10  
  Purchase #6 $96.34   9.828%   $105.8083   $105.81   $105.80   $105.80  
  Purchase #7 $125.68   7.231%   $134.7679   $134.77   $134.75   $134.80  
  7 purchase totals = $714.64       $770.1961   $770.20   $770.15   $770.10