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	$204.54	9.168%	$223.2922	$223.29	$223.30	$223.30
Purchase #2	$143.85	4.192%	$149.8802	$149.88	$149.90	$149.90
Purchase #3	$48.29	8.266%	$52.2817	$52.28	$52.30	$52.30
Purchase #4	$55.32	8.707%	$60.1367	$60.14	$60.15	$60.10
Purchase #5	$189.91	5.632%	$200.6057	$200.61	$200.60	$200.60
Purchase #6	$50.75	7.843%	$54.7303	$54.73	$54.75	$54.70
Purchase #7	$81.38	9.477%	$89.0924	$89.09	$89.10	$89.10
7 purchase totals =	$774.04		$830.0192	$830.02	$830.10	$830.00