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 $131.41   8.517%   $142.6022   $142.60   $142.60   $142.60  
  Purchase #2 $32.43   6.376%   $34.4977   $34.50   $34.50   $34.50  
  Purchase #3 $115.49   4.632%   $120.8395   $120.84   $120.85   $120.80  
  Purchase #4 $231.89   9.529%   $253.9868   $253.99   $254.00   $254.00  
  Purchase #5 $76.70   5.339%   $80.795   $80.80   $80.80   $80.80  
  Purchase #6 $183.91   11.682%   $205.3944   $205.39   $205.40   $205.40  
  Purchase #7 $225.59   6.728%   $240.7677   $240.77   $240.75   $240.80  
  7 purchase totals = $997.42       $1,078.8833   $1,078.89   $1,078.90   $1,078.90