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 $65.62   13.828%   $74.6939   $74.69   $74.70   $74.70  
  Purchase #2 $158.99   11.243%   $176.8652   $176.87   $176.85   $176.90  
  Purchase #3 $126.90   12.291%   $142.4973   $142.50   $142.50   $142.50  
  Purchase #4 $124.44   6.532%   $132.5684   $132.57   $132.55   $132.60  
  Purchase #5 $219.76   3.795%   $228.0999   $228.10   $228.10   $228.10  
  Purchase #6 $106.55   13.309%   $120.7307   $120.73   $120.75   $120.70  
  Purchase #7 $233.26   5.834%   $246.8684   $246.87   $246.85   $246.90  
  7 purchase totals = $1,035.52       $1,122.3238   $1,122.33   $1,122.30   $1,122.40