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	$214.44	6.859%	$229.1484	$229.15	$229.15	$229.10
Purchase #2	$101.44	12.788%	$114.4121	$114.41	$114.40	$114.40
Purchase #3	$82.87	9.169%	$90.4684	$90.47	$90.45	$90.50
Purchase #4	$84.80	11.254%	$94.3434	$94.34	$94.35	$94.30
Purchase #5	$40.65	13.424%	$46.1069	$46.11	$46.10	$46.10
Purchase #6	$73.28	8.564%	$79.5557	$79.56	$79.55	$79.60
Purchase #7	$100.73	10.540%	$111.3469	$111.35	$111.35	$111.30
7 purchase totals =	$698.21		$765.3818	$765.39	$765.35	$765.30