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	$40.60	4.107%	$42.2674	$42.27	$42.25	$42.30
Purchase #2	$153.30	10.569%	$169.5023	$169.50	$169.50	$169.50
Purchase #3	$95.88	13.125%	$108.4643	$108.46	$108.45	$108.50
Purchase #4	$66.76	9.227%	$72.9199	$72.92	$72.90	$72.90
Purchase #5	$91.46	5.630%	$96.6092	$96.61	$96.60	$96.60
Purchase #6	$216.61	4.263%	$225.8441	$225.84	$225.85	$225.80
Purchase #7	$99.89	4.325%	$104.2102	$104.21	$104.20	$104.20
7 purchase totals =	$764.50		$819.8174	$819.81	$819.75	$819.80