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	$208.56	10.411%	$230.2732	$230.27	$230.25	$230.30
Purchase #2	$116.53	10.601%	$128.8833	$128.88	$128.90	$128.90
Purchase #3	$174.60	9.479%	$191.1503	$191.15	$191.15	$191.20
Purchase #4	$49.73	10.286%	$54.8452	$54.85	$54.85	$54.80
Purchase #5	$234.58	7.419%	$251.9835	$251.98	$252.00	$252.00
Purchase #6	$102.99	7.797%	$111.0201	$111.02	$111.00	$111.00
Purchase #7	$87.27	4.168%	$90.9074	$90.91	$90.90	$90.90
7 purchase totals =	$974.26		$1,059.0630	$1,059.06	$1,059.05	$1,059.10