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	$82.25	13.407%	$93.2773	$93.28	$93.30	$93.30
Purchase #2	$192.30	3.275%	$198.5978	$198.60	$198.60	$198.60
Purchase #3	$216.80	9.621%	$237.6583	$237.66	$237.65	$237.70
Purchase #4	$160.73	3.151%	$165.7946	$165.79	$165.80	$165.80
Purchase #5	$100.41	3.727%	$104.1523	$104.15	$104.15	$104.20
Purchase #6	$82.47	8.616%	$89.5756	$89.58	$89.60	$89.60
Purchase #7	$95.76	3.658%	$99.2629	$99.26	$99.25	$99.30
7 purchase totals =	$930.72		$988.3188	$988.32	$988.35	$988.50