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 $140.99   10.842%   $156.2761   $156.28   $156.30   $156.30  
  Purchase #2 $205.94   8.697%   $223.8506   $223.85   $223.85   $223.90  
  Purchase #3 $92.63   5.197%   $97.444   $97.44   $97.45   $97.40  
  Purchase #4 $122.73   3.169%   $126.6193   $126.62   $126.60   $126.60  
  Purchase #5 $80.76   6.738%   $86.2016   $86.20   $86.20   $86.20  
  Purchase #6 $161.69   10.541%   $178.7337   $178.73   $178.75   $178.70  
  Purchase #7 $164.45   10.520%   $181.7501   $181.75   $181.75   $181.80  
  7 purchase totals = $969.19       $1,050.8754   $1,050.87   $1,050.90   $1,050.90