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 $208.81   10.797%   $231.3552   $231.36   $231.35   $231.40  
  Purchase #2 $26.36   13.831%   $30.0059   $30.01   $30.00   $30.00  
  Purchase #3 $34.45   11.693%   $38.4782   $38.48   $38.50   $38.50  
  Purchase #4 $44.80   7.614%   $48.2111   $48.21   $48.20   $48.20  
  Purchase #5 $98.60   13.465%   $111.8765   $111.88   $111.90   $111.90  
  Purchase #6 $118.48   9.856%   $130.1574   $130.16   $130.15   $130.20  
  Purchase #7 $250.99   8.631%   $272.6529   $272.65   $272.65   $272.70  
  7 purchase totals = $782.49       $862.7372   $862.75   $862.75   $862.90