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 $39.25   11.706%   $43.8446   $43.84   $43.85   $43.80  
  Purchase #2 $103.41   12.388%   $116.2204   $116.22   $116.20   $116.20  
  Purchase #3 $142.80   3.163%   $147.3168   $147.32   $147.30   $147.30  
  Purchase #4 $69.91   13.433%   $79.301   $79.30   $79.30   $79.30  
  Purchase #5 $209.60   5.863%   $221.8888   $221.89   $221.90   $221.90  
  Purchase #6 $111.86   13.246%   $126.677   $126.68   $126.70   $126.70  
  Purchase #7 $119.95   11.723%   $134.0117   $134.01   $134.00   $134.00  
  7 purchase totals = $796.78       $869.2603   $869.26   $869.25   $869.20