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	$170.45	13.178%	$192.9119	$192.91	$192.90	$192.90
Purchase #2	$198.53	12.635%	$223.6143	$223.61	$223.60	$223.60
Purchase #3	$166.51	11.418%	$185.5221	$185.52	$185.50	$185.50
Purchase #4	$222.36	10.461%	$245.6211	$245.62	$245.60	$245.60
Purchase #5	$191.96	4.841%	$201.2528	$201.25	$201.25	$201.30
Purchase #6	$137.50	12.669%	$154.9199	$154.92	$154.90	$154.90
Purchase #7	$107.76	3.680%	$111.7256	$111.73	$111.75	$111.70
7 purchase totals =	$1,195.07		$1,315.5677	$1,315.56	$1,315.50	$1,315.50