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	$88.86	12.653%	$100.1035	$100.10	$100.10	$100.10
Purchase #2	$59.56	5.523%	$62.8495	$62.85	$62.85	$62.80
Purchase #3	$55.60	9.867%	$61.0861	$61.09	$61.10	$61.10
Purchase #4	$217.58	12.502%	$244.7819	$244.78	$244.80	$244.80
Purchase #5	$209.87	9.333%	$229.4572	$229.46	$229.45	$229.50
Purchase #6	$157.79	4.613%	$165.0689	$165.07	$165.05	$165.10
Purchase #7	$209.97	6.591%	$223.8091	$223.81	$223.80	$223.80
7 purchase totals =	$999.23		$1,087.1562	$1,087.16	$1,087.15	$1,087.20