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 $82.59   3.823%   $85.7474   $85.75   $85.75   $85.70  
  Purchase #2 $127.47   4.150%   $132.76   $132.76   $132.75   $132.80  
  Purchase #3 $28.90   4.516%   $30.2051   $30.21   $30.20   $30.20  
  Purchase #4 $213.79   3.531%   $221.3389   $221.34   $221.35   $221.30  
  Purchase #5 $223.86   3.312%   $231.2742   $231.27   $231.25   $231.30  
  Purchase #6 $5.88   13.657%   $6.683   $6.68   $6.70   $6.70  
  Purchase #7 $46.54   7.233%   $49.9062   $49.91   $49.90   $49.90  
  7 purchase totals = $729.03       $757.9148   $757.92   $757.90   $757.90