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	$169.44	11.422%	$188.7934	$188.79	$188.80	$188.80
Purchase #2	$198.54	3.339%	$205.1693	$205.17	$205.15	$205.20
Purchase #3	$217.68	4.531%	$227.5431	$227.54	$227.55	$227.50
Purchase #4	$243.41	5.535%	$256.8827	$256.88	$256.90	$256.90
Purchase #5	$95.83	4.386%	$100.0331	$100.03	$100.05	$100.00
Purchase #6	$227.37	4.613%	$237.8586	$237.86	$237.85	$237.90
Purchase #7	$217.43	9.816%	$238.7729	$238.77	$238.75	$238.80
7 purchase totals =	$1,369.70		$1,455.0531	$1,455.04	$1,455.05	$1,455.10