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 $214.37   12.405%   $240.9626   $240.96   $240.95   $241.00  
  Purchase #2 $223.59   3.707%   $231.8785   $231.88   $231.90   $231.90  
  Purchase #3 $249.44   3.855%   $259.0559   $259.06   $259.05   $259.10  
  Purchase #4 $118.70   5.752%   $125.5276   $125.53   $125.55   $125.50  
  Purchase #5 $16.35   3.783%   $16.9685   $16.97   $16.95   $17.00  
  Purchase #6 $72.81   9.463%   $79.7   $79.70   $79.70   $79.70  
  Purchase #7 $91.89   4.782%   $96.2842   $96.28   $96.30   $96.30  
  7 purchase totals = $987.15       $1,050.3773   $1,050.38   $1,050.40   $1,050.50