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	$143.77	11.291%	$160.0031	$160.00	$160.00	$160.00
Purchase #2	$74.86	10.723%	$82.8872	$82.89	$82.90	$82.90
Purchase #3	$159.35	5.286%	$167.7732	$167.77	$167.75	$167.80
Purchase #4	$110.69	11.288%	$123.1847	$123.18	$123.20	$123.20
Purchase #5	$139.53	10.110%	$153.6365	$153.64	$153.65	$153.60
Purchase #6	$174.55	5.148%	$183.5358	$183.54	$183.55	$183.50
Purchase #7	$203.29	12.501%	$228.7033	$228.70	$228.70	$228.70
7 purchase totals =	$1,006.04		$1,099.7238	$1,099.72	$1,099.75	$1,099.70