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	$27.68	7.872%	$29.859	$29.86	$29.85	$29.90
Purchase #2	$205.38	13.582%	$233.2747	$233.27	$233.25	$233.30
Purchase #3	$126.29	5.538%	$133.2839	$133.28	$133.30	$133.30
Purchase #4	$39.38	7.361%	$42.2788	$42.28	$42.30	$42.30
Purchase #5	$154.29	13.262%	$174.7519	$174.75	$174.75	$174.80
Purchase #6	$73.28	13.571%	$83.2248	$83.22	$83.20	$83.20
Purchase #7	$101.64	11.699%	$113.5309	$113.53	$113.55	$113.50
7 purchase totals =	$727.94		$810.2040	$810.19	$810.20	$810.30