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	$122.37	4.338%	$127.6784	$127.68	$127.70	$127.70
Purchase #2	$196.59	9.571%	$215.4056	$215.41	$215.40	$215.40
Purchase #3	$240.59	13.170%	$272.2757	$272.28	$272.30	$272.30
Purchase #4	$104.72	4.211%	$109.1298	$109.13	$109.15	$109.10
Purchase #5	$17.69	9.258%	$19.3277	$19.33	$19.35	$19.30
Purchase #6	$126.86	8.702%	$137.8994	$137.90	$137.90	$137.90
Purchase #7	$48.37	12.226%	$54.2837	$54.28	$54.30	$54.30
7 purchase totals =	$857.19		$936.0003	$936.01	$936.10	$936.00