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	$199.72	11.563%	$222.8136	$222.81	$222.80	$222.80
Purchase #2	$83.83	10.319%	$92.4804	$92.48	$92.50	$92.50
Purchase #3	$242.72	11.766%	$271.2784	$271.28	$271.30	$271.30
Purchase #4	$105.35	6.307%	$111.9944	$111.99	$112.00	$112.00
Purchase #5	$56.62	5.631%	$59.8083	$59.81	$59.80	$59.80
Purchase #6	$15.77	9.586%	$17.2817	$17.28	$17.30	$17.30
Purchase #7	$55.63	7.327%	$59.706	$59.71	$59.70	$59.70
7 purchase totals =	$759.64		$835.3628	$835.36	$835.40	$835.40