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 $214.68   11.179%   $238.6791   $238.68   $238.70   $238.70  
  Purchase #2 $144.41   12.420%   $162.3457   $162.35   $162.35   $162.30  
  Purchase #3 $79.49   9.194%   $86.7983   $86.80   $86.80   $86.80  
  Purchase #4 $151.90   3.540%   $157.2773   $157.28   $157.30   $157.30  
  Purchase #5 $50.28   9.237%   $54.9244   $54.92   $54.90   $54.90  
  Purchase #6 $157.52   13.768%   $179.2074   $179.21   $179.20   $179.20  
  Purchase #7 $122.26   13.448%   $138.7015   $138.70   $138.70   $138.70  
  7 purchase totals = $920.54       $1,017.9337   $1,017.94   $1,017.95   $1,017.90