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 $219.94   6.163%   $233.4949   $233.49   $233.50   $233.50  
  Purchase #2 $175.63   5.382%   $185.0824   $185.08   $185.10   $185.10  
  Purchase #3 $195.71   9.155%   $213.6273   $213.63   $213.65   $213.60  
  Purchase #4 $246.36   7.631%   $265.1597   $265.16   $265.15   $265.20  
  Purchase #5 $233.80   7.763%   $251.9499   $251.95   $251.95   $251.90  
  Purchase #6 $53.63   9.365%   $58.6524   $58.65   $58.65   $58.70  
  Purchase #7 $54.53   7.559%   $58.6519   $58.65   $58.65   $58.70  
  7 purchase totals = $1,179.60       $1,266.6185   $1,266.61   $1,266.65   $1,266.70