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 $14.28   3.152%   $14.7301   $14.73   $14.75   $14.70  
  Purchase #2 $23.99   8.395%   $26.004   $26.00   $26.00   $26.00  
  Purchase #3 $161.41   3.440%   $166.9625   $166.96   $166.95   $167.00  
  Purchase #4 $222.69   8.164%   $240.8704   $240.87   $240.85   $240.90  
  Purchase #5 $113.38   8.272%   $122.7588   $122.76   $122.75   $122.80  
  Purchase #6 $205.80   3.307%   $212.6058   $212.61   $212.60   $212.60  
  Purchase #7 $61.32   3.584%   $63.5177   $63.52   $63.50   $63.50  
  7 purchase totals = $802.87       $847.4493   $847.45   $847.40   $847.50