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	$13.96	9.761%	$15.3226	$15.32	$15.30	$15.30
Purchase #2	$105.61	10.565%	$116.7677	$116.77	$116.75	$116.80
Purchase #3	$35.64	7.117%	$38.1765	$38.18	$38.20	$38.20
Purchase #4	$99.60	6.726%	$106.2991	$106.30	$106.30	$106.30
Purchase #5	$44.87	7.513%	$48.2411	$48.24	$48.25	$48.20
Purchase #6	$105.87	8.196%	$114.5471	$114.55	$114.55	$114.50
Purchase #7	$56.76	4.823%	$59.4975	$59.50	$59.50	$59.50
7 purchase totals =	$462.31		$498.8516	$498.86	$498.85	$498.80