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 $219.66   3.313%   $226.9373   $226.94   $226.95   $226.90  
  Purchase #2 $98.91   8.856%   $107.6695   $107.67   $107.65   $107.70  
  Purchase #3 $76.95   7.514%   $82.732   $82.73   $82.75   $82.70  
  Purchase #4 $9.45   8.502%   $10.2534   $10.25   $10.25   $10.30  
  Purchase #5 $55.29   11.833%   $61.8325   $61.83   $61.85   $61.80  
  Purchase #6 $220.30   11.533%   $245.7072   $245.71   $245.70   $245.70  
  Purchase #7 $80.40   7.104%   $86.1116   $86.11   $86.10   $86.10  
  7 purchase totals = $760.96       $821.2435   $821.24   $821.25   $821.20