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	$47.99	7.328%	$51.5067	$51.51	$51.50	$51.50
Purchase #2	$136.37	9.388%	$149.1724	$149.17	$149.15	$149.20
Purchase #3	$83.68	6.847%	$89.4096	$89.41	$89.40	$89.40
Purchase #4	$79.45	3.777%	$82.4508	$82.45	$82.45	$82.50
Purchase #5	$240.52	6.828%	$256.9427	$256.94	$256.95	$256.90
Purchase #6	$207.75	10.121%	$228.7764	$228.78	$228.80	$228.80
Purchase #7	$135.59	7.532%	$145.8026	$145.80	$145.80	$145.80
7 purchase totals =	$931.35		$1,004.0612	$1,004.06	$1,004.05	$1,004.10