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	$249.52	10.548%	$275.8394	$275.84	$275.85	$275.80
Purchase #2	$109.72	12.287%	$123.2013	$123.20	$123.20	$123.20
Purchase #3	$178.33	7.361%	$191.4569	$191.46	$191.45	$191.50
Purchase #4	$179.75	4.727%	$188.2468	$188.25	$188.25	$188.20
Purchase #5	$188.28	4.558%	$196.8618	$196.86	$196.85	$196.90
Purchase #6	$68.41	10.269%	$75.435	$75.44	$75.45	$75.40
Purchase #7	$94.79	13.527%	$107.6122	$107.61	$107.60	$107.60
7 purchase totals =	$1,068.80		$1,158.6534	$1,158.66	$1,158.65	$1,158.60