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	$79.77	10.778%	$88.3676	$88.37	$88.35	$88.40
Purchase #2	$133.44	11.400%	$148.6522	$148.65	$148.65	$148.70
Purchase #3	$16.53	8.522%	$17.9387	$17.94	$17.95	$17.90
Purchase #4	$89.32	12.540%	$100.5207	$100.52	$100.50	$100.50
Purchase #5	$184.72	5.311%	$194.5305	$194.53	$194.55	$194.50
Purchase #6	$141.30	9.781%	$155.1206	$155.12	$155.10	$155.10
Purchase #7	$79.69	12.864%	$89.9413	$89.94	$89.95	$89.90
7 purchase totals =	$724.77		$795.0716	$795.07	$795.05	$795.00