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 $236.53   3.136%   $243.9476   $243.95   $243.95   $243.90  
  Purchase #2 $32.85   5.326%   $34.5996   $34.60   $34.60   $34.60  
  Purchase #3 $165.30   9.421%   $180.8729   $180.87   $180.85   $180.90  
  Purchase #4 $47.62   5.761%   $50.3634   $50.36   $50.35   $50.40  
  Purchase #5 $199.70   4.189%   $208.0654   $208.07   $208.05   $208.10  
  Purchase #6 $9.30   9.662%   $10.1986   $10.20   $10.20   $10.20  
  Purchase #7 $17.76   4.418%   $18.5446   $18.54   $18.55   $18.50  
  7 purchase totals = $709.06       $746.5921   $746.59   $746.55   $746.60