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 $83.78   13.298%   $94.9211   $94.92   $94.90   $94.90  
  Purchase #2 $183.59   12.564%   $206.6562   $206.66   $206.65   $206.70  
  Purchase #3 $72.76   6.763%   $77.6808   $77.68   $77.70   $77.70  
  Purchase #4 $13.43   12.394%   $15.0945   $15.09   $15.10   $15.10  
  Purchase #5 $24.47   11.265%   $27.2265   $27.23   $27.25   $27.20  
  Purchase #6 $157.25   7.416%   $168.9117   $168.91   $168.90   $168.90  
  Purchase #7 $24.63   3.714%   $25.5448   $25.54   $25.55   $25.50  
  7 purchase totals = $559.91       $616.0356   $616.03   $616.05   $616.00