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	$45.39	11.164%	$50.4573	$50.46	$50.45	$50.50
Purchase #2	$176.77	6.522%	$188.2989	$188.30	$188.30	$188.30
Purchase #3	$96.96	6.318%	$103.0859	$103.09	$103.10	$103.10
Purchase #4	$32.72	7.734%	$35.2506	$35.25	$35.25	$35.30
Purchase #5	$75.84	8.755%	$82.4798	$82.48	$82.50	$82.50
Purchase #6	$118.92	13.643%	$135.1443	$135.14	$135.15	$135.10
Purchase #7	$241.52	13.231%	$273.4755	$273.48	$273.50	$273.50
7 purchase totals =	$788.12		$868.1923	$868.20	$868.25	$868.30