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 $54.43   5.466%   $57.4051   $57.41   $57.40   $57.40  
  Purchase #2 $120.54   3.154%   $124.3418   $124.34   $124.35   $124.30  
  Purchase #3 $68.44   13.460%   $77.652   $77.65   $77.65   $77.70  
  Purchase #4 $39.65   12.251%   $44.5075   $44.51   $44.50   $44.50  
  Purchase #5 $151.25   7.338%   $162.3487   $162.35   $162.35   $162.30  
  Purchase #6 $27.25   10.216%   $30.0339   $30.03   $30.05   $30.00  
  Purchase #7 $101.38   13.531%   $115.0977   $115.10   $115.10   $115.10  
  7 purchase totals = $562.94       $611.3867   $611.39   $611.40   $611.30