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	$129.72	12.691%	$146.1828	$146.18	$146.20	$146.20
Purchase #2	$37.28	7.622%	$40.1215	$40.12	$40.10	$40.10
Purchase #3	$249.83	3.381%	$258.2768	$258.28	$258.30	$258.30
Purchase #4	$223.66	6.734%	$238.7213	$238.72	$238.70	$238.70
Purchase #5	$11.97	11.262%	$13.3181	$13.32	$13.30	$13.30
Purchase #6	$168.39	9.764%	$184.8316	$184.83	$184.85	$184.80
Purchase #7	$190.91	12.461%	$214.6993	$214.70	$214.70	$214.70
7 purchase totals =	$1,011.76		$1,096.1514	$1,096.15	$1,096.15	$1,096.10