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	$69.61	11.293%	$77.4711	$77.47	$77.45	$77.50
Purchase #2	$228.36	6.807%	$243.9045	$243.90	$243.90	$243.90
Purchase #3	$238.87	7.449%	$256.6634	$256.66	$256.65	$256.70
Purchase #4	$31.84	8.357%	$34.5009	$34.50	$34.50	$34.50
Purchase #5	$48.26	12.515%	$54.2997	$54.30	$54.30	$54.30
Purchase #6	$44.55	4.611%	$46.6042	$46.60	$46.60	$46.60
Purchase #7	$57.26	3.565%	$59.3013	$59.30	$59.30	$59.30
7 purchase totals =	$718.75		$772.7451	$772.73	$772.70	$772.80