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	$204.40	9.170%	$223.1435	$223.14	$223.15	$223.10
Purchase #2	$108.70	5.531%	$114.7122	$114.71	$114.70	$114.70
Purchase #3	$108.40	13.834%	$123.3961	$123.40	$123.40	$123.40
Purchase #4	$171.38	8.374%	$185.7314	$185.73	$185.75	$185.70
Purchase #5	$179.38	5.422%	$189.106	$189.11	$189.10	$189.10
Purchase #6	$126.38	8.332%	$136.91	$136.91	$136.90	$136.90
Purchase #7	$102.95	13.514%	$116.8627	$116.86	$116.85	$116.90
7 purchase totals =	$1,001.59		$1,089.8619	$1,089.86	$1,089.85	$1,089.80