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 $214.46   11.839%   $239.8499   $239.85   $239.85   $239.80  
  Purchase #2 $193.25   3.497%   $200.008   $200.01   $200.00   $200.00  
  Purchase #3 $18.47   5.578%   $19.5003   $19.50   $19.50   $19.50  
  Purchase #4 $61.39   5.739%   $64.9132   $64.91   $64.90   $64.90  
  Purchase #5 $112.41   9.378%   $122.9518   $122.95   $122.95   $123.00  
  Purchase #6 $211.34   9.767%   $231.9816   $231.98   $232.00   $232.00  
  Purchase #7 $243.36   11.509%   $271.3683   $271.37   $271.35   $271.40  
  7 purchase totals = $1,054.68       $1,150.5731   $1,150.57   $1,150.55   $1,150.60