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 $76.29   12.707%   $85.9842   $85.98   $86.00   $86.00  
  Purchase #2 $25.30   3.378%   $26.1546   $26.15   $26.15   $26.20  
  Purchase #3 $172.80   11.234%   $192.2124   $192.21   $192.20   $192.20  
  Purchase #4 $10.26   8.820%   $11.1649   $11.16   $11.15   $11.20  
  Purchase #5 $207.73   3.739%   $215.497   $215.50   $215.50   $215.50  
  Purchase #6 $69.31   10.553%   $76.6243   $76.62   $76.60   $76.60  
  Purchase #7 $69.54   7.157%   $74.517   $74.52   $74.50   $74.50  
  7 purchase totals = $631.23       $682.1544   $682.14   $682.10   $682.20