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	$153.52	6.651%	$163.7306	$163.73	$163.75	$163.70
Purchase #2	$50.45	6.773%	$53.867	$53.87	$53.85	$53.90
Purchase #3	$85.52	4.577%	$89.4343	$89.43	$89.45	$89.40
Purchase #4	$93.96	7.801%	$101.2898	$101.29	$101.30	$101.30
Purchase #5	$48.50	10.860%	$53.7671	$53.77	$53.75	$53.80
Purchase #6	$138.50	4.436%	$144.6439	$144.64	$144.65	$144.60
Purchase #7	$223.45	4.200%	$232.8349	$232.83	$232.85	$232.80
7 purchase totals =	$793.90		$839.5676	$839.56	$839.60	$839.50