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	$37.37	13.769%	$42.5155	$42.52	$42.50	$42.50
Purchase #2	$181.74	5.373%	$191.5049	$191.50	$191.50	$191.50
Purchase #3	$37.79	4.321%	$39.4229	$39.42	$39.40	$39.40
Purchase #4	$43.60	11.847%	$48.7653	$48.77	$48.75	$48.80
Purchase #5	$24.88	5.385%	$26.2198	$26.22	$26.20	$26.20
Purchase #6	$38.29	13.816%	$43.5801	$43.58	$43.60	$43.60
Purchase #7	$46.94	7.252%	$50.3441	$50.34	$50.35	$50.30
7 purchase totals =	$410.61		$442.3526	$442.35	$442.30	$442.30