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	$90.88	11.631%	$101.4503	$101.45	$101.45	$101.50
Purchase #2	$176.42	5.722%	$186.5148	$186.51	$186.50	$186.50
Purchase #3	$134.37	9.104%	$146.603	$146.60	$146.60	$146.60
Purchase #4	$41.51	10.515%	$45.8748	$45.87	$45.85	$45.90
Purchase #5	$140.94	10.544%	$155.8007	$155.80	$155.80	$155.80
Purchase #6	$222.89	3.644%	$231.0121	$231.01	$231.00	$231.00
Purchase #7	$125.92	5.216%	$132.488	$132.49	$132.50	$132.50
7 purchase totals =	$932.93		$999.7437	$999.73	$999.70	$999.80