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	$151.77	9.786%	$166.6222	$166.62	$166.60	$166.60
Purchase #2	$198.45	9.174%	$216.6558	$216.66	$216.65	$216.70
Purchase #3	$19.88	7.558%	$21.3825	$21.38	$21.40	$21.40
Purchase #4	$24.86	10.336%	$27.4295	$27.43	$27.45	$27.40
Purchase #5	$102.58	13.433%	$116.3596	$116.36	$116.35	$116.40
Purchase #6	$25.43	11.418%	$28.3336	$28.33	$28.35	$28.30
Purchase #7	$42.44	7.321%	$45.547	$45.55	$45.55	$45.50
7 purchase totals =	$565.41		$622.3302	$622.33	$622.35	$622.30