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	$87.32	3.187%	$90.1029	$90.10	$90.10	$90.10
Purchase #2	$185.38	13.129%	$209.7185	$209.72	$209.70	$209.70
Purchase #3	$149.27	5.477%	$157.4455	$157.45	$157.45	$157.40
Purchase #4	$160.55	10.160%	$176.8619	$176.86	$176.85	$176.90
Purchase #5	$123.76	5.780%	$130.9133	$130.91	$130.90	$130.90
Purchase #6	$106.97	11.476%	$119.2459	$119.25	$119.25	$119.20
Purchase #7	$158.79	9.310%	$173.5733	$173.57	$173.55	$173.60
7 purchase totals =	$972.04		$1,057.8613	$1,057.86	$1,057.80	$1,057.80