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	$120.31	4.806%	$126.0921	$126.09	$126.10	$126.10
Purchase #2	$247.83	12.779%	$279.5002	$279.50	$279.50	$279.50
Purchase #3	$29.28	10.532%	$32.3638	$32.36	$32.35	$32.40
Purchase #4	$120.32	6.589%	$128.2479	$128.25	$128.25	$128.20
Purchase #5	$69.92	10.295%	$77.1183	$77.12	$77.10	$77.10
Purchase #6	$148.47	5.375%	$156.4503	$156.45	$156.45	$156.50
Purchase #7	$37.41	5.830%	$39.591	$39.59	$39.60	$39.60
7 purchase totals =	$773.54		$839.3636	$839.36	$839.35	$839.40