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	$41.45	9.651%	$45.4503	$45.45	$45.45	$45.50
Purchase #2	$39.74	9.467%	$43.5022	$43.50	$43.50	$43.50
Purchase #3	$248.37	7.667%	$267.4125	$267.41	$267.40	$267.40
Purchase #4	$85.52	12.837%	$96.4982	$96.50	$96.50	$96.50
Purchase #5	$47.83	3.253%	$49.3859	$49.39	$49.40	$49.40
Purchase #6	$31.34	13.565%	$35.5913	$35.59	$35.60	$35.60
Purchase #7	$58.84	10.622%	$65.09	$65.09	$65.10	$65.10
7 purchase totals =	$553.09		$602.9304	$602.93	$602.95	$603.00