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	$94.93	5.216%	$99.8815	$99.88	$99.90	$99.90
Purchase #2	$120.58	7.250%	$129.3221	$129.32	$129.30	$129.30
Purchase #3	$14.76	4.307%	$15.3957	$15.40	$15.40	$15.40
Purchase #4	$150.70	10.580%	$166.6441	$166.64	$166.65	$166.60
Purchase #5	$71.70	9.854%	$78.7653	$78.77	$78.75	$78.80
Purchase #6	$80.51	11.702%	$89.9313	$89.93	$89.95	$89.90
Purchase #7	$241.58	10.217%	$266.2622	$266.26	$266.25	$266.30
7 purchase totals =	$774.76		$846.2022	$846.20	$846.20	$846.20