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 $196.36   13.154%   $222.1892   $222.19   $222.20   $222.20  
  Purchase #2 $69.83   5.517%   $73.6825   $73.68   $73.70   $73.70  
  Purchase #3 $86.59   13.779%   $98.5212   $98.52   $98.50   $98.50  
  Purchase #4 $147.65   5.704%   $156.072   $156.07   $156.05   $156.10  
  Purchase #5 $119.39   4.112%   $124.2993   $124.30   $124.30   $124.30  
  Purchase #6 $51.52   9.143%   $56.2305   $56.23   $56.25   $56.20  
  Purchase #7 $122.77   3.203%   $126.7023   $126.70   $126.70   $126.70  
  7 purchase totals = $794.11       $857.6970   $857.69   $857.70   $857.70