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 $183.85   6.834%   $196.4143   $196.41   $196.40   $196.40  
  Purchase #2 $21.38   12.149%   $23.9775   $23.98   $24.00   $24.00  
  Purchase #3 $60.48   11.487%   $67.4273   $67.43   $67.45   $67.40  
  Purchase #4 $205.80   10.264%   $226.9233   $226.92   $226.90   $226.90  
  Purchase #5 $245.80   5.492%   $259.2993   $259.30   $259.30   $259.30  
  Purchase #6 $171.30   12.808%   $193.2401   $193.24   $193.25   $193.20  
  Purchase #7 $190.44   3.754%   $197.5891   $197.59   $197.60   $197.60  
  7 purchase totals = $1,079.05       $1,164.8709   $1,164.87   $1,164.90   $1,164.80