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	$249.51	11.808%	$278.9721	$278.97	$278.95	$279.00
Purchase #2	$70.58	3.271%	$72.8887	$72.89	$72.90	$72.90
Purchase #3	$50.49	8.111%	$54.5852	$54.59	$54.60	$54.60
Purchase #4	$118.30	9.574%	$129.626	$129.63	$129.65	$129.60
Purchase #5	$66.39	9.371%	$72.6114	$72.61	$72.60	$72.60
Purchase #6	$174.64	9.681%	$191.5469	$191.55	$191.55	$191.50
Purchase #7	$175.25	7.140%	$187.7629	$187.76	$187.75	$187.80
7 purchase totals =	$905.16		$987.9932	$988.00	$988.00	$988.00