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	$77.27	4.398%	$80.6683	$80.67	$80.65	$80.70
Purchase #2	$246.57	4.438%	$257.5128	$257.51	$257.50	$257.50
Purchase #3	$62.81	7.806%	$67.7129	$67.71	$67.70	$67.70
Purchase #4	$122.50	9.861%	$134.5797	$134.58	$134.60	$134.60
Purchase #5	$27.59	3.321%	$28.5063	$28.51	$28.50	$28.50
Purchase #6	$80.70	10.617%	$89.2679	$89.27	$89.25	$89.30
Purchase #7	$74.44	5.494%	$78.5297	$78.53	$78.55	$78.50
7 purchase totals =	$691.88		$736.7776	$736.78	$736.75	$736.80