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	$53.79	5.738%	$56.8765	$56.88	$56.90	$56.90
Purchase #2	$95.36	12.463%	$107.2447	$107.24	$107.25	$107.20
Purchase #3	$225.75	11.435%	$251.5645	$251.56	$251.55	$251.60
Purchase #4	$123.95	11.196%	$137.8274	$137.83	$137.85	$137.80
Purchase #5	$144.41	9.613%	$158.2921	$158.29	$158.30	$158.30
Purchase #6	$183.61	9.376%	$200.8253	$200.83	$200.85	$200.80
Purchase #7	$144.54	7.689%	$155.6537	$155.65	$155.65	$155.70
7 purchase totals =	$971.41		$1,068.2842	$1,068.28	$1,068.35	$1,068.30