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	$28.31	6.185%	$30.061	$30.06	$30.05	$30.10
Purchase #2	$58.43	6.378%	$62.1567	$62.16	$62.15	$62.20
Purchase #3	$18.72	7.592%	$20.1412	$20.14	$20.15	$20.10
Purchase #4	$116.92	9.595%	$128.1385	$128.14	$128.15	$128.10
Purchase #5	$53.98	9.811%	$59.276	$59.28	$59.30	$59.30
Purchase #6	$175.51	3.286%	$181.2773	$181.28	$181.30	$181.30
Purchase #7	$68.77	4.744%	$72.0324	$72.03	$72.05	$72.00
7 purchase totals =	$520.64		$553.0831	$553.09	$553.15	$553.10