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	$74.61	5.873%	$78.9918	$78.99	$79.00	$79.00
Purchase #2	$98.60	13.234%	$111.6487	$111.65	$111.65	$111.60
Purchase #3	$114.53	11.663%	$127.8876	$127.89	$127.90	$127.90
Purchase #4	$176.70	3.555%	$182.9817	$182.98	$183.00	$183.00
Purchase #5	$160.40	9.690%	$175.9428	$175.94	$175.95	$175.90
Purchase #6	$134.62	13.739%	$153.1154	$153.12	$153.10	$153.10
Purchase #7	$77.96	10.501%	$86.1466	$86.15	$86.15	$86.10
7 purchase totals =	$837.42		$916.7146	$916.72	$916.75	$916.60