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	$81.73	9.249%	$89.2892	$89.29	$89.30	$89.30
Purchase #2	$101.85	6.404%	$108.3725	$108.37	$108.35	$108.40
Purchase #3	$107.69	13.831%	$122.5846	$122.58	$122.60	$122.60
Purchase #4	$134.46	7.661%	$144.761	$144.76	$144.75	$144.80
Purchase #5	$197.56	8.713%	$214.7734	$214.77	$214.75	$214.80
Purchase #6	$234.55	8.134%	$253.6283	$253.63	$253.65	$253.60
Purchase #7	$154.33	8.127%	$166.8724	$166.87	$166.85	$166.90
7 purchase totals =	$1,012.17		$1,100.2814	$1,100.27	$1,100.25	$1,100.40