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 $24.90   5.584%   $26.2904   $26.29   $26.30   $26.30  
  Purchase #2 $113.86   3.243%   $117.5525   $117.55   $117.55   $117.60  
  Purchase #3 $66.46   12.132%   $74.5229   $74.52   $74.50   $74.50  
  Purchase #4 $13.85   4.835%   $14.5196   $14.52   $14.50   $14.50  
  Purchase #5 $40.37   6.510%   $42.9981   $43.00   $43.00   $43.00  
  Purchase #6 $214.87   10.376%   $237.1649   $237.16   $237.15   $237.20  
  Purchase #7 $150.39   13.705%   $171.0009   $171.00   $171.00   $171.00  
  7 purchase totals = $624.70       $684.0493   $684.04   $684.00   $684.10