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	$35.48	7.697%	$38.2109	$38.21	$38.20	$38.20
Purchase #2	$226.38	13.450%	$256.8281	$256.83	$256.85	$256.80
Purchase #3	$128.86	4.629%	$134.8249	$134.82	$134.80	$134.80
Purchase #4	$247.50	4.789%	$259.3528	$259.35	$259.35	$259.40
Purchase #5	$56.41	7.214%	$60.4794	$60.48	$60.50	$60.50
Purchase #6	$233.66	10.462%	$258.1055	$258.11	$258.10	$258.10
Purchase #7	$133.59	9.670%	$146.5082	$146.51	$146.50	$146.50
7 purchase totals =	$1,061.88		$1,154.3098	$1,154.31	$1,154.30	$1,154.30