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	$103.35	6.286%	$109.8466	$109.85	$109.85	$109.80
Purchase #2	$72.66	7.722%	$78.2708	$78.27	$78.25	$78.30
Purchase #3	$215.43	3.781%	$223.5754	$223.58	$223.60	$223.60
Purchase #4	$76.83	3.601%	$79.5966	$79.60	$79.60	$79.60
Purchase #5	$100.52	7.105%	$107.6619	$107.66	$107.65	$107.70
Purchase #6	$210.93	11.381%	$234.9359	$234.94	$234.95	$234.90
Purchase #7	$246.51	12.865%	$278.2235	$278.22	$278.20	$278.20
7 purchase totals =	$1,026.23		$1,112.1107	$1,112.12	$1,112.10	$1,112.10