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	$250.56	9.848%	$275.2351	$275.24	$275.25	$275.20
Purchase #2	$165.41	4.157%	$172.2861	$172.29	$172.30	$172.30
Purchase #3	$93.68	7.668%	$100.8634	$100.86	$100.85	$100.90
Purchase #4	$150.66	13.469%	$170.9524	$170.95	$170.95	$171.00
Purchase #5	$233.44	9.494%	$255.6028	$255.60	$255.60	$255.60
Purchase #6	$188.78	4.131%	$196.5785	$196.58	$196.60	$196.60
Purchase #7	$31.39	8.459%	$34.0453	$34.05	$34.05	$34.00
7 purchase totals =	$1,113.92		$1,205.5636	$1,205.57	$1,205.60	$1,205.60