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	$131.56	10.717%	$145.6593	$145.66	$145.65	$145.70
Purchase #2	$19.81	8.664%	$21.5263	$21.53	$21.55	$21.50
Purchase #3	$176.86	13.437%	$200.6247	$200.62	$200.60	$200.60
Purchase #4	$123.28	8.831%	$134.1669	$134.17	$134.15	$134.20
Purchase #5	$165.31	5.549%	$174.4831	$174.48	$174.50	$174.50
Purchase #6	$78.62	3.501%	$81.3725	$81.37	$81.35	$81.40
Purchase #7	$167.88	7.378%	$180.2662	$180.27	$180.25	$180.30
7 purchase totals =	$863.32		$938.0990	$938.10	$938.05	$938.20