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 $5.29   13.769%   $6.0184   $6.02   $6.00   $6.00  
  Purchase #2 $60.87   7.263%   $65.291   $65.29   $65.30   $65.30  
  Purchase #3 $247.52   5.770%   $261.8019   $261.80   $261.80   $261.80  
  Purchase #4 $108.89   10.156%   $119.9489   $119.95   $119.95   $119.90  
  Purchase #5 $102.90   3.788%   $106.7979   $106.80   $106.80   $106.80  
  Purchase #6 $119.77   13.773%   $136.2659   $136.27   $136.25   $136.30  
  Purchase #7 $72.93   5.373%   $76.8485   $76.85   $76.85   $76.80  
  7 purchase totals = $718.17       $772.9725   $772.98   $772.95   $772.90