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	$60.47	6.233%	$64.2391	$64.24	$64.25	$64.20
Purchase #2	$143.85	7.315%	$154.3726	$154.37	$154.35	$154.40
Purchase #3	$57.68	6.510%	$61.435	$61.44	$61.45	$61.40
Purchase #4	$175.86	10.823%	$194.8933	$194.89	$194.90	$194.90
Purchase #5	$34.81	13.550%	$39.5268	$39.53	$39.55	$39.50
Purchase #6	$19.96	4.734%	$20.9049	$20.90	$20.90	$20.90
Purchase #7	$89.53	7.239%	$96.0111	$96.01	$96.00	$96.00
7 purchase totals =	$582.16		$631.3828	$631.38	$631.40	$631.30