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	$21.74	7.218%	$23.3092	$23.31	$23.30	$23.30
Purchase #2	$63.47	9.441%	$69.4622	$69.46	$69.45	$69.50
Purchase #3	$146.96	10.219%	$161.9778	$161.98	$162.00	$162.00
Purchase #4	$103.75	7.144%	$111.1619	$111.16	$111.15	$111.20
Purchase #5	$233.56	9.486%	$255.7155	$255.72	$255.70	$255.70
Purchase #6	$152.83	13.517%	$173.488	$173.49	$173.50	$173.50
Purchase #7	$177.27	12.293%	$199.0618	$199.06	$199.05	$199.10
7 purchase totals =	$899.58		$994.1764	$994.18	$994.15	$994.30