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	$40.65	6.128%	$43.141	$43.14	$43.15	$43.10
Purchase #2	$115.29	4.260%	$120.2014	$120.20	$120.20	$120.20
Purchase #3	$19.58	5.333%	$20.6242	$20.62	$20.60	$20.60
Purchase #4	$98.90	5.282%	$104.1239	$104.12	$104.10	$104.10
Purchase #5	$40.52	7.129%	$43.4087	$43.41	$43.40	$43.40
Purchase #6	$148.29	5.491%	$156.4326	$156.43	$156.45	$156.40
Purchase #7	$18.62	12.438%	$20.936	$20.94	$20.95	$20.90
7 purchase totals =	$481.85		$508.8678	$508.86	$508.85	$508.70