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	$80.91	10.532%	$89.4314	$89.43	$89.45	$89.40
Purchase #2	$112.67	4.785%	$118.0613	$118.06	$118.05	$118.10
Purchase #3	$54.92	12.550%	$61.8125	$61.81	$61.80	$61.80
Purchase #4	$186.30	13.128%	$210.7575	$210.76	$210.75	$210.80
Purchase #5	$181.25	5.603%	$191.4054	$191.41	$191.40	$191.40
Purchase #6	$18.57	6.625%	$19.8003	$19.80	$19.80	$19.80
Purchase #7	$34.52	4.285%	$35.9992	$36.00	$36.00	$36.00
7 purchase totals =	$669.14		$727.2676	$727.27	$727.25	$727.30