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 $12.52   13.513%   $14.2118   $14.21   $14.20   $14.20  
  Purchase #2 $169.85   3.613%   $175.9867   $175.99   $176.00   $176.00  
  Purchase #3 $96.74   5.239%   $101.8082   $101.81   $101.80   $101.80  
  Purchase #4 $10.55   4.401%   $11.0143   $11.01   $11.00   $11.00  
  Purchase #5 $29.86   3.389%   $30.872   $30.87   $30.85   $30.90  
  Purchase #6 $86.29   8.484%   $93.6108   $93.61   $93.60   $93.60  
  Purchase #7 $229.55   12.838%   $259.0196   $259.02   $259.00   $259.00  
  7 purchase totals = $635.36       $686.5234   $686.52   $686.45   $686.50