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	$78.51	13.648%	$89.225	$89.23	$89.25	$89.20
Purchase #2	$103.51	13.627%	$117.6153	$117.62	$117.60	$117.60
Purchase #3	$123.65	6.565%	$131.7676	$131.77	$131.75	$131.80
Purchase #4	$64.46	3.106%	$66.4621	$66.46	$66.45	$66.50
Purchase #5	$160.62	9.559%	$175.9737	$175.97	$175.95	$176.00
Purchase #6	$103.47	3.412%	$107.0004	$107.00	$107.00	$107.00
Purchase #7	$161.33	7.608%	$173.604	$173.60	$173.60	$173.60
7 purchase totals =	$795.55		$861.6481	$861.65	$861.60	$861.70