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 $205.71   5.226%   $216.4604   $216.46   $216.45   $216.50  
  Purchase #2 $57.77   9.292%   $63.138   $63.14   $63.15   $63.10  
  Purchase #3 $11.58   7.352%   $12.4314   $12.43   $12.45   $12.40  
  Purchase #4 $230.40   9.874%   $253.1497   $253.15   $253.15   $253.10  
  Purchase #5 $187.64   10.558%   $207.451   $207.45   $207.45   $207.50  
  Purchase #6 $223.53   8.626%   $242.8117   $242.81   $242.80   $242.80  
  Purchase #7 $13.64   10.452%   $15.0657   $15.07   $15.05   $15.10  
  7 purchase totals = $930.27       $1,010.5079   $1,010.51   $1,010.50   $1,010.50