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	$67.52	10.340%	$74.5016	$74.50	$74.50	$74.50
Purchase #2	$137.37	7.697%	$147.9434	$147.94	$147.95	$147.90
Purchase #3	$89.50	12.331%	$100.5362	$100.54	$100.55	$100.50
Purchase #4	$174.50	9.839%	$191.6691	$191.67	$191.65	$191.70
Purchase #5	$143.85	10.355%	$158.7457	$158.75	$158.75	$158.70
Purchase #6	$7.30	8.727%	$7.9371	$7.94	$7.95	$7.90
Purchase #7	$127.54	3.278%	$131.7208	$131.72	$131.70	$131.70
7 purchase totals =	$747.58		$813.0539	$813.06	$813.05	$812.90