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 $57.34   7.477%   $61.6273   $61.63   $61.65   $61.60  
  Purchase #2 $143.49   13.439%   $162.7736   $162.77   $162.75   $162.80  
  Purchase #3 $197.40   9.805%   $216.7551   $216.76   $216.75   $216.80  
  Purchase #4 $90.95   5.318%   $95.7867   $95.79   $95.80   $95.80  
  Purchase #5 $227.30   6.105%   $241.1767   $241.18   $241.20   $241.20  
  Purchase #6 $52.37   9.180%   $57.1776   $57.18   $57.20   $57.20  
  Purchase #7 $155.84   9.464%   $170.5887   $170.59   $170.60   $170.60  
  7 purchase totals = $924.69       $1,005.8857   $1,005.90   $1,005.95   $1,006.00