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 $153.69   9.759%   $168.6886   $168.69   $168.70   $168.70  
  Purchase #2 $23.45   10.872%   $25.9995   $26.00   $26.00   $26.00  
  Purchase #3 $93.90   5.227%   $98.8082   $98.81   $98.80   $98.80  
  Purchase #4 $195.86   5.309%   $206.2582   $206.26   $206.25   $206.30  
  Purchase #5 $235.87   7.371%   $253.256   $253.26   $253.25   $253.30  
  Purchase #6 $191.75   11.413%   $213.6344   $213.63   $213.65   $213.60  
  Purchase #7 $46.53   8.669%   $50.5637   $50.56   $50.55   $50.60  
  7 purchase totals = $941.05       $1,017.2086   $1,017.21   $1,017.20   $1,017.30