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	$80.27	10.276%	$88.5185	$88.52	$88.50	$88.50
Purchase #2	$112.97	13.174%	$127.8527	$127.85	$127.85	$127.90
Purchase #3	$210.31	3.123%	$216.878	$216.88	$216.90	$216.90
Purchase #4	$135.72	4.457%	$141.769	$141.77	$141.75	$141.80
Purchase #5	$58.98	13.476%	$66.9281	$66.93	$66.95	$66.90
Purchase #6	$215.27	6.842%	$229.9988	$230.00	$230.00	$230.00
Purchase #7	$112.51	5.637%	$118.8522	$118.85	$118.85	$118.90
7 purchase totals =	$926.03		$990.7973	$990.80	$990.80	$990.90