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 $146.92   13.602%   $166.9041   $166.90   $166.90   $166.90  
  Purchase #2 $77.68   12.461%   $87.3597   $87.36   $87.35   $87.40  
  Purchase #3 $205.37   9.215%   $224.2948   $224.29   $224.30   $224.30  
  Purchase #4 $137.76   6.561%   $146.7984   $146.80   $146.80   $146.80  
  Purchase #5 $147.86   6.324%   $157.2107   $157.21   $157.20   $157.20  
  Purchase #6 $111.43   4.248%   $116.1635   $116.16   $116.15   $116.20  
  Purchase #7 $117.40   5.361%   $123.6938   $123.69   $123.70   $123.70  
  7 purchase totals = $944.42       $1,022.4250   $1,022.41   $1,022.40   $1,022.50