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	$49.79	12.300%	$55.9142	$55.91	$55.90	$55.90
Purchase #2	$36.49	13.465%	$41.4034	$41.40	$41.40	$41.40
Purchase #3	$235.75	4.308%	$245.9061	$245.91	$245.90	$245.90
Purchase #4	$37.29	7.479%	$40.0789	$40.08	$40.10	$40.10
Purchase #5	$74.94	3.297%	$77.4108	$77.41	$77.40	$77.40
Purchase #6	$37.32	3.389%	$38.5848	$38.58	$38.60	$38.60
Purchase #7	$105.92	5.577%	$111.8272	$111.83	$111.85	$111.80
7 purchase totals =	$577.50		$611.1254	$611.12	$611.15	$611.10