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	$79.28	13.624%	$90.0811	$90.08	$90.10	$90.10
Purchase #2	$241.66	10.419%	$266.8386	$266.84	$266.85	$266.80
Purchase #3	$46.96	4.251%	$48.9563	$48.96	$48.95	$49.00
Purchase #4	$84.40	5.769%	$89.269	$89.27	$89.25	$89.30
Purchase #5	$214.40	6.147%	$227.5792	$227.58	$227.60	$227.60
Purchase #6	$249.39	9.748%	$273.7005	$273.70	$273.70	$273.70
Purchase #7	$51.58	4.850%	$54.0816	$54.08	$54.10	$54.10
7 purchase totals =	$967.67		$1,050.5063	$1,050.51	$1,050.55	$1,050.60