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	$55.69	7.309%	$59.7604	$59.76	$59.75	$59.80
Purchase #2	$127.53	8.658%	$138.5715	$138.57	$138.55	$138.60
Purchase #3	$122.41	13.346%	$138.7468	$138.75	$138.75	$138.70
Purchase #4	$143.50	9.640%	$157.3334	$157.33	$157.35	$157.30
Purchase #5	$100.90	10.765%	$111.7619	$111.76	$111.75	$111.80
Purchase #6	$15.59	12.402%	$17.5235	$17.52	$17.50	$17.50
Purchase #7	$113.70	5.143%	$119.5476	$119.55	$119.55	$119.50
7 purchase totals =	$679.32		$743.2451	$743.24	$743.20	$743.20