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 $55.52   11.620%   $61.9714   $61.97   $61.95   $62.00  
  Purchase #2 $227.94   12.429%   $256.2707   $256.27   $256.25   $256.30  
  Purchase #3 $136.71   10.464%   $151.0153   $151.02   $151.00   $151.00  
  Purchase #4 $82.89   4.634%   $86.7311   $86.73   $86.75   $86.70  
  Purchase #5 $122.31   9.437%   $133.8524   $133.85   $133.85   $133.90  
  Purchase #6 $70.53   9.646%   $77.3333   $77.33   $77.35   $77.30  
  Purchase #7 $81.68   8.610%   $88.7126   $88.71   $88.70   $88.70  
  7 purchase totals = $777.58       $855.8868   $855.88   $855.85   $855.90