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	$12.76	8.215%	$13.8082	$13.81	$13.80	$13.80
Purchase #2	$17.39	8.433%	$18.8565	$18.86	$18.85	$18.90
Purchase #3	$131.85	10.855%	$146.1623	$146.16	$146.15	$146.20
Purchase #4	$48.59	5.200%	$51.1167	$51.12	$51.10	$51.10
Purchase #5	$40.99	5.310%	$43.1666	$43.17	$43.15	$43.20
Purchase #6	$31.33	3.501%	$32.4269	$32.43	$32.45	$32.40
Purchase #7	$29.33	13.646%	$33.3324	$33.33	$33.35	$33.30
7 purchase totals =	$312.24		$338.8696	$338.88	$338.85	$338.90