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	$48.92	3.153%	$50.4624	$50.46	$50.45	$50.50
Purchase #2	$126.51	11.737%	$141.3585	$141.36	$141.35	$141.40
Purchase #3	$159.30	9.282%	$174.0862	$174.09	$174.10	$174.10
Purchase #4	$29.93	3.745%	$31.0509	$31.05	$31.05	$31.10
Purchase #5	$41.74	13.240%	$47.2664	$47.27	$47.25	$47.30
Purchase #6	$173.60	12.244%	$194.8556	$194.86	$194.85	$194.90
Purchase #7	$77.85	6.367%	$82.8067	$82.81	$82.80	$82.80
7 purchase totals =	$657.85		$721.8867	$721.90	$721.85	$722.10