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 $240.80   6.203%   $255.7368   $255.74   $255.75   $255.70  
  Purchase #2 $119.34   9.450%   $130.6176   $130.62   $130.60   $130.60  
  Purchase #3 $214.89   7.410%   $230.8133   $230.81   $230.80   $230.80  
  Purchase #4 $55.99   8.133%   $60.5437   $60.54   $60.55   $60.50  
  Purchase #5 $205.31   6.606%   $218.8728   $218.87   $218.85   $218.90  
  Purchase #6 $69.36   5.340%   $73.0638   $73.06   $73.05   $73.10  
  Purchase #7 $42.40   5.477%   $44.7222   $44.72   $44.70   $44.70  
  7 purchase totals = $948.09       $1,014.3702   $1,014.36   $1,014.30   $1,014.30