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 $183.86   13.237%   $208.1975   $208.20   $208.20   $208.20  
  Purchase #2 $186.52   5.447%   $196.6797   $196.68   $196.70   $196.70  
  Purchase #3 $179.71   10.695%   $198.93   $198.93   $198.95   $198.90  
  Purchase #4 $87.64   11.178%   $97.4364   $97.44   $97.45   $97.40  
  Purchase #5 $160.80   4.219%   $167.5842   $167.58   $167.60   $167.60  
  Purchase #6 $177.76   8.786%   $193.378   $193.38   $193.40   $193.40  
  Purchase #7 $22.69   10.823%   $25.1457   $25.15   $25.15   $25.10  
  7 purchase totals = $998.98       $1,087.3515   $1,087.36   $1,087.45   $1,087.30