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 $239.50   7.706%   $257.9559   $257.96   $257.95   $258.00  
  Purchase #2 $43.96   10.757%   $48.6888   $48.69   $48.70   $48.70  
  Purchase #3 $189.52   13.776%   $215.6283   $215.63   $215.65   $215.60  
  Purchase #4 $245.99   10.522%   $271.8731   $271.87   $271.85   $271.90  
  Purchase #5 $113.88   3.139%   $117.4547   $117.45   $117.45   $117.50  
  Purchase #6 $150.72   3.497%   $155.9907   $155.99   $156.00   $156.00  
  Purchase #7 $85.49   11.147%   $95.0196   $95.02   $95.00   $95.00  
  7 purchase totals = $1,069.06       $1,162.6111   $1,162.61   $1,162.60   $1,162.70