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 $68.70   5.557%   $72.5177   $72.52   $72.50   $72.50  
  Purchase #2 $171.99   8.336%   $186.3271   $186.33   $186.35   $186.30  
  Purchase #3 $98.83   13.422%   $112.095   $112.10   $112.10   $112.10  
  Purchase #4 $151.61   8.874%   $165.0639   $165.06   $165.05   $165.10  
  Purchase #5 $126.36   3.574%   $130.8761   $130.88   $130.90   $130.90  
  Purchase #6 $28.34   5.811%   $29.9868   $29.99   $30.00   $30.00  
  Purchase #7 $157.68   8.511%   $171.1001   $171.10   $171.10   $171.10  
  7 purchase totals = $803.51       $867.9667   $867.98   $868.00   $868.00