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	$31.75	4.746%	$33.2569	$33.26	$33.25	$33.30
Purchase #2	$141.72	9.622%	$155.3563	$155.36	$155.35	$155.40
Purchase #3	$104.59	4.339%	$109.1282	$109.13	$109.15	$109.10
Purchase #4	$90.82	9.328%	$99.2917	$99.29	$99.30	$99.30
Purchase #5	$11.79	5.281%	$12.4126	$12.41	$12.40	$12.40
Purchase #6	$32.91	4.747%	$34.4722	$34.47	$34.45	$34.50
Purchase #7	$58.47	11.660%	$65.2876	$65.29	$65.30	$65.30
7 purchase totals =	$472.05		$509.2055	$509.21	$509.20	$509.30