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 $24.80   7.363%   $26.626   $26.63   $26.65   $26.60  
  Purchase #2 $180.34   6.511%   $192.0819   $192.08   $192.10   $192.10  
  Purchase #3 $42.99   9.551%   $47.096   $47.10   $47.10   $47.10  
  Purchase #4 $153.68   13.327%   $174.1609   $174.16   $174.15   $174.20  
  Purchase #5 $26.89   6.389%   $28.608   $28.61   $28.60   $28.60  
  Purchase #6 $242.41   8.286%   $262.4961   $262.50   $262.50   $262.50  
  Purchase #7 $92.94   8.737%   $101.0602   $101.06   $101.05   $101.10  
  7 purchase totals = $764.05       $832.1291   $832.14   $832.15   $832.20