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	$45.62	12.506%	$51.3252	$51.33	$51.35	$51.30
Purchase #2	$181.28	3.849%	$188.2575	$188.26	$188.25	$188.30
Purchase #3	$193.29	7.753%	$208.2758	$208.28	$208.30	$208.30
Purchase #4	$228.35	11.864%	$255.4414	$255.44	$255.45	$255.40
Purchase #5	$153.83	5.417%	$162.163	$162.16	$162.15	$162.20
Purchase #6	$211.72	9.863%	$232.6019	$232.60	$232.60	$232.60
Purchase #7	$48.93	7.309%	$52.5063	$52.51	$52.50	$52.50
7 purchase totals =	$1,063.02		$1,150.5711	$1,150.58	$1,150.60	$1,150.60