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	$137.63	12.657%	$155.0498	$155.05	$155.05	$155.00
Purchase #2	$65.59	9.125%	$71.5751	$71.58	$71.60	$71.60
Purchase #3	$141.77	11.802%	$158.5017	$158.50	$158.50	$158.50
Purchase #4	$91.58	11.858%	$102.4396	$102.44	$102.45	$102.40
Purchase #5	$32.28	10.661%	$35.7214	$35.72	$35.70	$35.70
Purchase #6	$204.72	10.423%	$226.058	$226.06	$226.05	$226.10
Purchase #7	$154.57	11.671%	$172.6099	$172.61	$172.60	$172.60
7 purchase totals =	$828.14		$921.9555	$921.96	$921.95	$921.90