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	$74.56	10.426%	$82.3336	$82.33	$82.35	$82.30
Purchase #2	$130.90	5.770%	$138.4529	$138.45	$138.45	$138.50
Purchase #3	$48.85	9.605%	$53.542	$53.54	$53.55	$53.50
Purchase #4	$80.72	6.403%	$85.8885	$85.89	$85.90	$85.90
Purchase #5	$72.78	10.118%	$80.1439	$80.14	$80.15	$80.10
Purchase #6	$21.85	4.272%	$22.7834	$22.78	$22.80	$22.80
Purchase #7	$62.51	6.682%	$66.6869	$66.69	$66.70	$66.70
7 purchase totals =	$492.17		$529.8312	$529.82	$529.90	$529.80