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	$219.75	8.851%	$239.2001	$239.20	$239.20	$239.20
Purchase #2	$55.61	6.246%	$59.0834	$59.08	$59.10	$59.10
Purchase #3	$149.46	6.688%	$159.4559	$159.46	$159.45	$159.50
Purchase #4	$133.76	13.335%	$151.5969	$151.60	$151.60	$151.60
Purchase #5	$82.93	8.627%	$90.0844	$90.08	$90.10	$90.10
Purchase #6	$243.39	4.159%	$253.5126	$253.51	$253.50	$253.50
Purchase #7	$164.96	8.211%	$178.5049	$178.50	$178.50	$178.50
7 purchase totals =	$1,049.86		$1,131.4382	$1,131.43	$1,131.45	$1,131.50