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	$122.66	4.123%	$127.7173	$127.72	$127.70	$127.70
Purchase #2	$192.75	8.601%	$209.3284	$209.33	$209.35	$209.30
Purchase #3	$151.35	4.573%	$158.2712	$158.27	$158.25	$158.30
Purchase #4	$153.52	8.576%	$166.6859	$166.69	$166.70	$166.70
Purchase #5	$237.29	12.203%	$266.2465	$266.25	$266.25	$266.20
Purchase #6	$51.63	12.203%	$57.9304	$57.93	$57.95	$57.90
Purchase #7	$99.36	13.490%	$112.7637	$112.76	$112.75	$112.80
7 purchase totals =	$1,008.56		$1,098.9434	$1,098.95	$1,098.95	$1,098.90