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 $204.72   4.593%   $214.1228   $214.12   $214.10   $214.10  
  Purchase #2 $64.92   12.839%   $73.2551   $73.26   $73.25   $73.30  
  Purchase #3 $82.47   5.170%   $86.7337   $86.73   $86.75   $86.70  
  Purchase #4 $109.44   6.247%   $116.2767   $116.28   $116.30   $116.30  
  Purchase #5 $213.86   4.829%   $224.1873   $224.19   $224.20   $224.20  
  Purchase #6 $41.94   13.683%   $47.6787   $47.68   $47.70   $47.70  
  Purchase #7 $245.69   12.597%   $276.6396   $276.64   $276.65   $276.60  
  7 purchase totals = $963.04       $1,038.8939   $1,038.90   $1,038.95   $1,038.90