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	$102.89	13.180%	$116.4509	$116.45	$116.45	$116.50
Purchase #2	$72.72	6.328%	$77.3217	$77.32	$77.30	$77.30
Purchase #3	$136.64	12.310%	$153.4604	$153.46	$153.45	$153.50
Purchase #4	$208.91	9.476%	$228.7063	$228.71	$228.70	$228.70
Purchase #5	$53.72	12.491%	$60.4302	$60.43	$60.45	$60.40
Purchase #6	$56.84	9.507%	$62.2438	$62.24	$62.25	$62.20
Purchase #7	$64.70	9.621%	$70.9248	$70.92	$70.90	$70.90
7 purchase totals =	$696.42		$769.5381	$769.53	$769.50	$769.50