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	$13.60	9.295%	$14.8641	$14.86	$14.85	$14.90
Purchase #2	$128.58	8.761%	$139.8449	$139.84	$139.85	$139.80
Purchase #3	$129.44	9.772%	$142.0889	$142.09	$142.10	$142.10
Purchase #4	$62.47	3.104%	$64.4091	$64.41	$64.40	$64.40
Purchase #5	$27.45	10.286%	$30.2735	$30.27	$30.25	$30.30
Purchase #6	$40.50	11.824%	$45.2887	$45.29	$45.30	$45.30
Purchase #7	$105.69	6.569%	$112.6328	$112.63	$112.65	$112.60
7 purchase totals =	$507.73		$549.4020	$549.39	$549.40	$549.40