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	$151.94	5.250%	$159.9169	$159.92	$159.90	$159.90
Purchase #2	$185.58	11.328%	$206.6025	$206.60	$206.60	$206.60
Purchase #3	$121.30	13.319%	$137.4559	$137.46	$137.45	$137.50
Purchase #4	$96.51	9.661%	$105.8338	$105.83	$105.85	$105.80
Purchase #5	$31.82	4.234%	$33.1673	$33.17	$33.15	$33.20
Purchase #6	$104.25	11.518%	$116.2575	$116.26	$116.25	$116.30
Purchase #7	$14.55	7.190%	$15.5961	$15.60	$15.60	$15.60
7 purchase totals =	$705.95		$774.8300	$774.84	$774.80	$774.90