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	$154.56	12.258%	$173.506	$173.51	$173.50	$173.50
Purchase #2	$37.34	8.597%	$40.5501	$40.55	$40.55	$40.60
Purchase #3	$216.72	6.521%	$230.8523	$230.85	$230.85	$230.90
Purchase #4	$115.63	10.576%	$127.859	$127.86	$127.85	$127.90
Purchase #5	$110.98	7.871%	$119.7152	$119.72	$119.70	$119.70
Purchase #6	$166.94	12.458%	$187.7374	$187.74	$187.75	$187.70
Purchase #7	$131.81	13.701%	$149.8693	$149.87	$149.85	$149.90
7 purchase totals =	$933.98		$1,030.0893	$1,030.10	$1,030.05	$1,030.20