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	$54.52	3.589%	$56.4767	$56.48	$56.50	$56.50
Purchase #2	$59.64	4.841%	$62.5272	$62.53	$62.55	$62.50
Purchase #3	$231.46	3.812%	$240.2833	$240.28	$240.30	$240.30
Purchase #4	$246.31	6.749%	$262.9335	$262.93	$262.95	$262.90
Purchase #5	$230.60	12.566%	$259.5772	$259.58	$259.60	$259.60
Purchase #6	$99.45	4.403%	$103.8288	$103.83	$103.85	$103.80
Purchase #7	$69.28	11.491%	$77.241	$77.24	$77.25	$77.20
7 purchase totals =	$991.26		$1,062.8677	$1,062.87	$1,063.00	$1,062.80