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	$59.39	11.111%	$65.9888	$65.99	$66.00	$66.00
Purchase #2	$17.50	5.131%	$18.3979	$18.40	$18.40	$18.40
Purchase #3	$19.32	4.418%	$20.1736	$20.17	$20.15	$20.20
Purchase #4	$209.59	6.350%	$222.899	$222.90	$222.90	$222.90
Purchase #5	$54.68	4.829%	$57.3205	$57.32	$57.30	$57.30
Purchase #6	$233.95	4.470%	$244.4076	$244.41	$244.40	$244.40
Purchase #7	$53.91	5.641%	$56.9511	$56.95	$56.95	$57.00
7 purchase totals =	$648.34		$686.1385	$686.14	$686.10	$686.20