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	$50.64	13.469%	$57.4607	$57.46	$57.45	$57.50
Purchase #2	$64.27	12.408%	$72.2446	$72.24	$72.25	$72.20
Purchase #3	$21.56	4.825%	$22.6003	$22.60	$22.60	$22.60
Purchase #4	$72.66	7.251%	$77.9286	$77.93	$77.95	$77.90
Purchase #5	$208.65	6.616%	$222.4543	$222.45	$222.45	$222.50
Purchase #6	$143.43	8.215%	$155.2128	$155.21	$155.20	$155.20
Purchase #7	$77.95	5.166%	$81.9769	$81.98	$82.00	$82.00
7 purchase totals =	$639.16		$689.8782	$689.87	$689.90	$689.90