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	$122.82	6.867%	$131.254	$131.25	$131.25	$131.30
Purchase #2	$109.42	6.612%	$116.6549	$116.65	$116.65	$116.70
Purchase #3	$181.41	6.723%	$193.6062	$193.61	$193.60	$193.60
Purchase #4	$166.85	10.598%	$184.5328	$184.53	$184.55	$184.50
Purchase #5	$46.35	12.680%	$52.2272	$52.23	$52.25	$52.20
Purchase #6	$29.88	10.641%	$33.0595	$33.06	$33.05	$33.10
Purchase #7	$82.62	11.493%	$92.1155	$92.12	$92.10	$92.10
7 purchase totals =	$739.35		$803.4501	$803.45	$803.45	$803.50