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	$249.89	5.373%	$263.3166	$263.32	$263.30	$263.30
Purchase #2	$150.48	10.662%	$166.5242	$166.52	$166.50	$166.50
Purchase #3	$38.65	7.354%	$41.4923	$41.49	$41.50	$41.50
Purchase #4	$71.92	8.812%	$78.2576	$78.26	$78.25	$78.30
Purchase #5	$217.73	9.367%	$238.1248	$238.12	$238.10	$238.10
Purchase #6	$55.74	3.739%	$57.8241	$57.82	$57.80	$57.80
Purchase #7	$138.36	4.355%	$144.3856	$144.39	$144.40	$144.40
7 purchase totals =	$922.77		$989.9252	$989.92	$989.85	$989.90