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	$145.86	13.849%	$166.0602	$166.06	$166.05	$166.10
Purchase #2	$83.72	3.373%	$86.5439	$86.54	$86.55	$86.50
Purchase #3	$55.35	13.516%	$62.8311	$62.83	$62.85	$62.80
Purchase #4	$242.81	12.379%	$272.8674	$272.87	$272.85	$272.90
Purchase #5	$131.76	11.355%	$146.7213	$146.72	$146.70	$146.70
Purchase #6	$16.44	10.480%	$18.1629	$18.16	$18.15	$18.20
Purchase #7	$181.26	3.418%	$187.4555	$187.46	$187.45	$187.50
7 purchase totals =	$857.20		$940.6423	$940.64	$940.60	$940.70