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	$229.70	11.820%	$256.8505	$256.85	$256.85	$256.90
Purchase #2	$74.30	10.580%	$82.1609	$82.16	$82.15	$82.20
Purchase #3	$45.52	3.363%	$47.0508	$47.05	$47.05	$47.10
Purchase #4	$40.58	7.588%	$43.6592	$43.66	$43.65	$43.70
Purchase #5	$128.47	6.736%	$137.1237	$137.12	$137.10	$137.10
Purchase #6	$21.33	13.240%	$24.1541	$24.15	$24.15	$24.20
Purchase #7	$211.62	6.564%	$225.5107	$225.51	$225.50	$225.50
7 purchase totals =	$751.52		$816.5099	$816.50	$816.45	$816.70