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 $68.33   11.512%   $76.1961   $76.20   $76.20   $76.20  
  Purchase #2 $177.27   8.833%   $192.9283   $192.93   $192.95   $192.90  
  Purchase #3 $214.67   13.534%   $243.7234   $243.72   $243.70   $243.70  
  Purchase #4 $19.71   3.325%   $20.3654   $20.37   $20.35   $20.40  
  Purchase #5 $19.85   9.705%   $21.7764   $21.78   $21.80   $21.80  
  Purchase #6 $242.86   3.423%   $251.1731   $251.17   $251.15   $251.20  
  Purchase #7 $58.67   9.653%   $64.3334   $64.33   $64.35   $64.30  
  7 purchase totals = $801.36       $870.4961   $870.50   $870.50   $870.50