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 $152.70   7.567%   $164.2548   $164.25   $164.25   $164.30  
  Purchase #2 $213.62   9.377%   $233.6511   $233.65   $233.65   $233.70  
  Purchase #3 $155.73   9.193%   $170.0463   $170.05   $170.05   $170.00  
  Purchase #4 $13.35   3.723%   $13.847   $13.85   $13.85   $13.80  
  Purchase #5 $111.70   12.373%   $125.5206   $125.52   $125.50   $125.50  
  Purchase #6 $97.89   10.218%   $107.8924   $107.89   $107.90   $107.90  
  Purchase #7 $174.67   7.537%   $187.8349   $187.83   $187.85   $187.80  
  7 purchase totals = $919.66       $1,003.0471   $1,003.04   $1,003.05   $1,003.00