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 $208.60   8.583%   $226.5041   $226.50   $226.50   $226.50  
  Purchase #2 $241.56   6.838%   $258.0779   $258.08   $258.10   $258.10  
  Purchase #3 $212.73   10.326%   $234.6965   $234.70   $234.70   $234.70  
  Purchase #4 $180.45   9.654%   $197.8706   $197.87   $197.85   $197.90  
  Purchase #5 $44.84   7.624%   $48.2586   $48.26   $48.25   $48.30  
  Purchase #6 $106.73   4.349%   $111.3717   $111.37   $111.35   $111.40  
  Purchase #7 $235.60   5.526%   $248.6193   $248.62   $248.60   $248.60  
  7 purchase totals = $1,230.51       $1,325.3987   $1,325.40   $1,325.35   $1,325.50