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 $32.87   11.298%   $36.5837   $36.58   $36.60   $36.60  
  Purchase #2 $163.46   8.194%   $176.8539   $176.85   $176.85   $176.90  
  Purchase #3 $77.26   12.571%   $86.9724   $86.97   $86.95   $87.00  
  Purchase #4 $248.49   9.114%   $271.1374   $271.14   $271.15   $271.10  
  Purchase #5 $26.25   11.670%   $29.3134   $29.31   $29.30   $29.30  
  Purchase #6 $88.82   13.666%   $100.9581   $100.96   $100.95   $101.00  
  Purchase #7 $40.56   7.374%   $43.5509   $43.55   $43.55   $43.60  
  7 purchase totals = $677.71       $745.3698   $745.36   $745.35   $745.50