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 $112.44   8.603%   $122.1132   $122.11   $122.10   $122.10  
  Purchase #2 $21.74   11.227%   $24.1807   $24.18   $24.20   $24.20  
  Purchase #3 $226.51   13.134%   $256.2598   $256.26   $256.25   $256.30  
  Purchase #4 $180.71   5.339%   $190.3581   $190.36   $190.35   $190.40  
  Purchase #5 $156.76   5.525%   $165.421   $165.42   $165.40   $165.40  
  Purchase #6 $89.55   10.114%   $98.6071   $98.61   $98.60   $98.60  
  Purchase #7 $200.83   10.174%   $221.2624   $221.26   $221.25   $221.30  
  7 purchase totals = $988.54       $1,078.2023   $1,078.20   $1,078.15   $1,078.30