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	$211.78	12.728%	$238.7354	$238.74	$238.75	$238.70
Purchase #2	$102.77	11.597%	$114.6882	$114.69	$114.70	$114.70
Purchase #3	$241.77	12.331%	$271.5827	$271.58	$271.60	$271.60
Purchase #4	$245.77	8.420%	$266.4638	$266.46	$266.45	$266.50
Purchase #5	$165.48	3.451%	$171.1907	$171.19	$171.20	$171.20
Purchase #6	$100.27	11.307%	$111.6075	$111.61	$111.60	$111.60
Purchase #7	$50.49	3.585%	$52.3001	$52.30	$52.30	$52.30
7 purchase totals =	$1,118.33		$1,226.5684	$1,226.57	$1,226.60	$1,226.60