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	$29.76	12.429%	$33.4589	$33.46	$33.45	$33.50
Purchase #2	$129.37	12.478%	$145.5128	$145.51	$145.50	$145.50
Purchase #3	$206.65	10.533%	$228.4164	$228.42	$228.40	$228.40
Purchase #4	$27.54	8.109%	$29.7732	$29.77	$29.75	$29.80
Purchase #5	$118.84	7.577%	$127.8445	$127.84	$127.85	$127.80
Purchase #6	$92.94	3.610%	$96.2951	$96.30	$96.30	$96.30
Purchase #7	$211.46	10.800%	$234.2977	$234.30	$234.30	$234.30
7 purchase totals =	$816.56		$895.5986	$895.60	$895.55	$895.60