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	$9.98	6.338%	$10.6125	$10.61	$10.60	$10.60
Purchase #2	$70.65	10.841%	$78.3092	$78.31	$78.30	$78.30
Purchase #3	$215.56	4.704%	$225.6999	$225.70	$225.70	$225.70
Purchase #4	$42.35	9.262%	$46.2725	$46.27	$46.25	$46.30
Purchase #5	$26.80	6.400%	$28.5152	$28.52	$28.50	$28.50
Purchase #6	$211.72	5.625%	$223.6293	$223.63	$223.65	$223.60
Purchase #7	$9.54	5.788%	$10.0922	$10.09	$10.10	$10.10
7 purchase totals =	$586.60		$623.1308	$623.13	$623.10	$623.10