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	$239.49	3.811%	$248.617	$248.62	$248.60	$248.60
Purchase #2	$154.55	7.169%	$165.6297	$165.63	$165.65	$165.60
Purchase #3	$118.42	10.692%	$131.0815	$131.08	$131.10	$131.10
Purchase #4	$160.62	11.769%	$179.5234	$179.52	$179.50	$179.50
Purchase #5	$58.80	11.636%	$65.642	$65.64	$65.65	$65.60
Purchase #6	$142.47	7.215%	$152.7492	$152.75	$152.75	$152.70
Purchase #7	$35.78	13.279%	$40.5312	$40.53	$40.55	$40.50
7 purchase totals =	$910.13		$983.7740	$983.77	$983.80	$983.60