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	$136.32	12.615%	$153.5168	$153.52	$153.50	$153.50
Purchase #2	$91.82	10.673%	$101.6199	$101.62	$101.60	$101.60
Purchase #3	$94.49	5.222%	$99.4243	$99.42	$99.40	$99.40
Purchase #4	$179.62	6.554%	$191.3923	$191.39	$191.40	$191.40
Purchase #5	$239.25	8.387%	$259.3159	$259.32	$259.30	$259.30
Purchase #6	$129.74	11.230%	$144.3098	$144.31	$144.30	$144.30
Purchase #7	$185.33	12.433%	$208.3721	$208.37	$208.35	$208.40
7 purchase totals =	$1,056.57		$1,157.9511	$1,157.95	$1,157.85	$1,157.90