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 $86.69   13.298%   $98.218   $98.22   $98.20   $98.20  
  Purchase #2 $239.55   5.346%   $252.3563   $252.36   $252.35   $252.40  
  Purchase #3 $111.37   10.430%   $122.9859   $122.99   $123.00   $123.00  
  Purchase #4 $98.54   8.468%   $106.8844   $106.88   $106.90   $106.90  
  Purchase #5 $167.95   10.230%   $185.1313   $185.13   $185.15   $185.10  
  Purchase #6 $202.60   13.241%   $229.4263   $229.43   $229.45   $229.40  
  Purchase #7 $99.98   11.616%   $111.5937   $111.59   $111.60   $111.60  
  7 purchase totals = $1,006.68       $1,106.5959   $1,106.60   $1,106.65   $1,106.60