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	$86.69	9.840%	$95.2203	$95.22	$95.20	$95.20
Purchase #2	$34.77	9.485%	$38.0679	$38.07	$38.05	$38.10
Purchase #3	$217.73	7.218%	$233.4458	$233.45	$233.45	$233.40
Purchase #4	$164.46	9.872%	$180.6955	$180.70	$180.70	$180.70
Purchase #5	$170.37	8.521%	$184.8872	$184.89	$184.90	$184.90
Purchase #6	$144.67	4.723%	$151.5028	$151.50	$151.50	$151.50
Purchase #7	$81.69	9.590%	$89.5241	$89.52	$89.50	$89.50
7 purchase totals =	$900.38		$973.3436	$973.35	$973.30	$973.30