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 $12.42   13.826%   $14.1372   $14.14   $14.15   $14.10  
  Purchase #2 $215.44   13.373%   $244.2508   $244.25   $244.25   $244.30  
  Purchase #3 $71.76   3.843%   $74.5177   $74.52   $74.50   $74.50  
  Purchase #4 $66.90   10.722%   $74.073   $74.07   $74.05   $74.10  
  Purchase #5 $239.89   4.768%   $251.328   $251.33   $251.35   $251.30  
  Purchase #6 $74.86   10.262%   $82.5421   $82.54   $82.55   $82.50  
  Purchase #7 $88.29   7.774%   $95.1537   $95.15   $95.15   $95.20  
  7 purchase totals = $769.56       $836.0025   $836.00   $836.00   $836.00