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	$30.39	8.420%	$32.9488	$32.95	$32.95	$32.90
Purchase #2	$180.35	7.852%	$194.5111	$194.51	$194.50	$194.50
Purchase #3	$169.32	8.250%	$183.2889	$183.29	$183.30	$183.30
Purchase #4	$222.88	5.717%	$235.622	$235.62	$235.60	$235.60
Purchase #5	$40.50	13.219%	$45.8537	$45.85	$45.85	$45.90
Purchase #6	$31.27	12.445%	$35.1616	$35.16	$35.15	$35.20
Purchase #7	$105.41	11.203%	$117.2191	$117.22	$117.20	$117.20
7 purchase totals =	$780.12		$844.6052	$844.60	$844.55	$844.60