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 $161.66   7.325%   $173.5016   $173.50   $173.50   $173.50  
  Purchase #2 $242.50   10.112%   $267.0216   $267.02   $267.00   $267.00  
  Purchase #3 $96.55   9.304%   $105.533   $105.53   $105.55   $105.50  
  Purchase #4 $79.44   7.186%   $85.1486   $85.15   $85.15   $85.10  
  Purchase #5 $112.43   6.247%   $119.4535   $119.45   $119.45   $119.50  
  Purchase #6 $95.97   4.374%   $100.1677   $100.17   $100.15   $100.20  
  Purchase #7 $154.93   11.799%   $173.2102   $173.21   $173.20   $173.20  
  7 purchase totals = $943.48       $1,024.0362   $1,024.03   $1,024.00   $1,024.00