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 $56.62   11.698%   $63.2434   $63.24   $63.25   $63.20  
  Purchase #2 $245.99   6.526%   $262.0433   $262.04   $262.05   $262.00  
  Purchase #3 $155.25   4.516%   $162.2611   $162.26   $162.25   $162.30  
  Purchase #4 $18.29   9.362%   $20.0023   $20.00   $20.00   $20.00  
  Purchase #5 $59.94   5.848%   $63.4453   $63.45   $63.45   $63.40  
  Purchase #6 $17.62   3.453%   $18.2284   $18.23   $18.25   $18.20  
  Purchase #7 $138.51   12.606%   $155.9706   $155.97   $155.95   $156.00  
  7 purchase totals = $692.22       $745.1944   $745.19   $745.20   $745.10