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 $148.51   10.606%   $164.261   $164.26   $164.25   $164.30  
  Purchase #2 $53.26   10.493%   $58.8486   $58.85   $58.85   $58.80  
  Purchase #3 $50.75   5.622%   $53.6032   $53.60   $53.60   $53.60  
  Purchase #4 $201.71   9.816%   $221.5099   $221.51   $221.50   $221.50  
  Purchase #5 $178.33   11.172%   $198.253   $198.25   $198.25   $198.30  
  Purchase #6 $227.36   13.536%   $258.1354   $258.14   $258.15   $258.10  
  Purchase #7 $11.51   9.380%   $12.5896   $12.59   $12.60   $12.60  
  7 purchase totals = $871.43       $967.2007   $967.20   $967.20   $967.20