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 $48.86   12.693%   $55.0618   $55.06   $55.05   $55.10  
  Purchase #2 $245.88   6.784%   $262.5605   $262.56   $262.55   $262.60  
  Purchase #3 $101.62   3.754%   $105.4348   $105.43   $105.45   $105.40  
  Purchase #4 $195.41   11.774%   $218.4176   $218.42   $218.40   $218.40  
  Purchase #5 $213.87   8.177%   $231.3581   $231.36   $231.35   $231.40  
  Purchase #6 $142.91   7.435%   $153.5354   $153.54   $153.55   $153.50  
  Purchase #7 $19.62   8.790%   $21.3446   $21.34   $21.35   $21.30  
  7 purchase totals = $968.17       $1,047.7128   $1,047.71   $1,047.70   $1,047.70