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	$230.33	8.334%	$249.5257	$249.53	$249.55	$249.50
Purchase #2	$101.34	4.204%	$105.6003	$105.60	$105.60	$105.60
Purchase #3	$84.61	7.527%	$90.9786	$90.98	$91.00	$91.00
Purchase #4	$120.78	6.651%	$128.8131	$128.81	$128.80	$128.80
Purchase #5	$133.79	13.354%	$151.6563	$151.66	$151.65	$151.70
Purchase #6	$99.87	11.640%	$111.4949	$111.49	$111.50	$111.50
Purchase #7	$48.84	9.172%	$53.3196	$53.32	$53.30	$53.30
7 purchase totals =	$819.56		$891.3885	$891.39	$891.40	$891.40