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	$111.80	6.289%	$118.8311	$118.83	$118.85	$118.80
Purchase #2	$173.42	10.262%	$191.2164	$191.22	$191.20	$191.20
Purchase #3	$62.68	4.791%	$65.683	$65.68	$65.70	$65.70
Purchase #4	$134.70	4.812%	$141.1818	$141.18	$141.20	$141.20
Purchase #5	$133.96	10.508%	$148.0365	$148.04	$148.05	$148.00
Purchase #6	$86.41	7.131%	$92.5719	$92.57	$92.55	$92.60
Purchase #7	$158.98	7.577%	$171.0259	$171.03	$171.05	$171.00
7 purchase totals =	$861.95		$928.5466	$928.55	$928.60	$928.50