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	$155.50	11.598%	$173.5349	$173.53	$173.55	$173.50
Purchase #2	$83.54	6.651%	$89.0962	$89.10	$89.10	$89.10
Purchase #3	$47.28	13.612%	$53.7158	$53.72	$53.70	$53.70
Purchase #4	$79.97	13.673%	$90.9043	$90.90	$90.90	$90.90
Purchase #5	$113.26	8.711%	$123.1261	$123.13	$123.15	$123.10
Purchase #6	$83.70	6.345%	$89.0108	$89.01	$89.00	$89.00
Purchase #7	$151.33	4.769%	$158.5469	$158.55	$158.55	$158.50
7 purchase totals =	$714.58		$777.9350	$777.94	$777.95	$777.80