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 $56.98   11.589%   $63.5834   $63.58   $63.60   $63.60  
  Purchase #2 $98.83   10.628%   $109.3337   $109.33   $109.35   $109.30  
  Purchase #3 $109.78   4.785%   $115.033   $115.03   $115.05   $115.00  
  Purchase #4 $178.75   10.461%   $197.449   $197.45   $197.45   $197.40  
  Purchase #5 $52.28   9.257%   $57.1196   $57.12   $57.10   $57.10  
  Purchase #6 $224.98   13.113%   $254.4816   $254.48   $254.50   $254.50  
  Purchase #7 $23.42   13.460%   $26.5723   $26.57   $26.55   $26.60  
  7 purchase totals = $745.02       $823.5726   $823.56   $823.60   $823.50