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	$89.34	3.325%	$92.3106	$92.31	$92.30	$92.30
Purchase #2	$186.29	13.434%	$211.3162	$211.32	$211.30	$211.30
Purchase #3	$218.98	3.842%	$227.3932	$227.39	$227.40	$227.40
Purchase #4	$171.50	3.808%	$178.0307	$178.03	$178.05	$178.00
Purchase #5	$33.99	5.105%	$35.7252	$35.73	$35.75	$35.70
Purchase #6	$62.45	4.348%	$65.1653	$65.17	$65.15	$65.20
Purchase #7	$148.29	13.729%	$168.6487	$168.65	$168.65	$168.60
7 purchase totals =	$910.84		$978.5899	$978.60	$978.60	$978.50