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 $168.27   8.655%   $182.8338   $182.83   $182.85   $182.80  
  Purchase #2 $237.38   13.379%   $269.1391   $269.14   $269.15   $269.10  
  Purchase #3 $17.30   8.850%   $18.8311   $18.83   $18.85   $18.80  
  Purchase #4 $139.47   8.822%   $151.774   $151.77   $151.75   $151.80  
  Purchase #5 $95.60   10.873%   $105.9946   $105.99   $106.00   $106.00  
  Purchase #6 $158.60   10.764%   $175.6717   $175.67   $175.65   $175.70  
  Purchase #7 $88.85   6.653%   $94.7612   $94.76   $94.75   $94.80  
  7 purchase totals = $905.47       $999.0055   $998.99   $999.00   $999.00