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	$173.67	8.780%	$188.9182	$188.92	$188.90	$188.90
Purchase #2	$37.39	3.292%	$38.6209	$38.62	$38.60	$38.60
Purchase #3	$190.25	13.329%	$215.6084	$215.61	$215.60	$215.60
Purchase #4	$249.68	3.248%	$257.7896	$257.79	$257.80	$257.80
Purchase #5	$88.85	13.578%	$100.9141	$100.91	$100.90	$100.90
Purchase #6	$39.28	11.292%	$43.7155	$43.72	$43.70	$43.70
Purchase #7	$228.82	4.249%	$238.5426	$238.54	$238.55	$238.50
7 purchase totals =	$1,007.94		$1,084.1093	$1,084.11	$1,084.05	$1,084.00