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	$145.32	9.293%	$158.8246	$158.82	$158.80	$158.80
Purchase #2	$228.93	8.549%	$248.5012	$248.50	$248.50	$248.50
Purchase #3	$59.50	10.271%	$65.6112	$65.61	$65.60	$65.60
Purchase #4	$104.84	13.774%	$119.2807	$119.28	$119.30	$119.30
Purchase #5	$73.25	7.275%	$78.5789	$78.58	$78.60	$78.60
Purchase #6	$142.55	11.539%	$158.9988	$159.00	$159.00	$159.00
Purchase #7	$144.80	8.754%	$157.4758	$157.48	$157.50	$157.50
7 purchase totals =	$899.19		$987.2712	$987.27	$987.30	$987.30