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 $76.96   12.178%   $86.3322   $86.33   $86.35   $86.30  
  Purchase #2 $188.36   13.562%   $213.9054   $213.91   $213.90   $213.90  
  Purchase #3 $66.98   9.491%   $73.3371   $73.34   $73.35   $73.30  
  Purchase #4 $114.70   3.291%   $118.4748   $118.47   $118.45   $118.50  
  Purchase #5 $207.58   13.130%   $234.8353   $234.84   $234.85   $234.80  
  Purchase #6 $49.66   13.816%   $56.521   $56.52   $56.50   $56.50  
  Purchase #7 $83.57   8.155%   $90.3851   $90.39   $90.40   $90.40  
  7 purchase totals = $787.81       $873.7909   $873.80   $873.80   $873.70