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 $247.34   7.147%   $265.0174   $265.02   $265.00   $265.00  
  Purchase #2 $193.37   6.133%   $205.2294   $205.23   $205.25   $205.20  
  Purchase #3 $233.65   12.386%   $262.5899   $262.59   $262.60   $262.60  
  Purchase #4 $18.80   4.564%   $19.658   $19.66   $19.65   $19.70  
  Purchase #5 $153.51   11.374%   $170.9702   $170.97   $170.95   $171.00  
  Purchase #6 $96.34   13.655%   $109.4952   $109.50   $109.50   $109.50  
  Purchase #7 $6.38   6.685%   $6.8065   $6.81   $6.80   $6.80  
  7 purchase totals = $949.39       $1,039.7666   $1,039.78   $1,039.75   $1,039.80