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	$86.30	3.255%	$89.1091	$89.11	$89.10	$89.10
Purchase #2	$200.38	10.342%	$221.1033	$221.10	$221.10	$221.10
Purchase #3	$136.58	11.728%	$152.5981	$152.60	$152.60	$152.60
Purchase #4	$63.34	4.564%	$66.2308	$66.23	$66.25	$66.20
Purchase #5	$211.67	8.725%	$230.1382	$230.14	$230.15	$230.10
Purchase #6	$247.32	12.181%	$277.446	$277.45	$277.45	$277.40
Purchase #7	$47.28	9.823%	$51.9243	$51.92	$51.90	$51.90
7 purchase totals =	$992.87		$1,088.5498	$1,088.55	$1,088.55	$1,088.40