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	$245.60	13.631%	$279.0777	$279.08	$279.10	$279.10
Purchase #2	$93.67	12.642%	$105.5118	$105.51	$105.50	$105.50
Purchase #3	$62.92	4.616%	$65.8244	$65.82	$65.80	$65.80
Purchase #4	$21.78	10.360%	$24.0364	$24.04	$24.05	$24.00
Purchase #5	$154.87	3.458%	$160.2254	$160.23	$160.25	$160.20
Purchase #6	$216.70	12.764%	$244.3596	$244.36	$244.35	$244.40
Purchase #7	$135.39	12.171%	$151.8683	$151.87	$151.85	$151.90
7 purchase totals =	$930.93		$1,030.9036	$1,030.91	$1,030.90	$1,030.90