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	$32.71	11.729%	$36.5466	$36.55	$36.55	$36.50
Purchase #2	$76.50	7.512%	$82.2467	$82.25	$82.25	$82.20
Purchase #3	$226.37	11.631%	$252.6991	$252.70	$252.70	$252.70
Purchase #4	$126.76	11.651%	$141.5288	$141.53	$141.55	$141.50
Purchase #5	$183.39	13.459%	$208.0725	$208.07	$208.05	$208.10
Purchase #6	$234.86	8.874%	$255.7015	$255.70	$255.70	$255.70
Purchase #7	$106.86	4.623%	$111.8001	$111.80	$111.80	$111.80
7 purchase totals =	$987.45		$1,088.5953	$1,088.60	$1,088.60	$1,088.50