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	$230.42	5.796%	$243.7751	$243.78	$243.80	$243.80
Purchase #2	$125.80	3.672%	$130.4194	$130.42	$130.40	$130.40
Purchase #3	$167.30	7.322%	$179.5497	$179.55	$179.55	$179.50
Purchase #4	$230.97	10.763%	$255.8293	$255.83	$255.85	$255.80
Purchase #5	$99.45	12.136%	$111.5193	$111.52	$111.50	$111.50
Purchase #6	$54.77	10.102%	$60.3029	$60.30	$60.30	$60.30
Purchase #7	$196.94	11.426%	$219.4424	$219.44	$219.45	$219.40
7 purchase totals =	$1,105.65		$1,200.8381	$1,200.84	$1,200.85	$1,200.70