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	$237.85	9.776%	$261.1022	$261.10	$261.10	$261.10
Purchase #2	$56.59	8.647%	$61.4833	$61.48	$61.50	$61.50
Purchase #3	$235.88	12.141%	$264.5182	$264.52	$264.50	$264.50
Purchase #4	$43.71	7.221%	$46.8663	$46.87	$46.85	$46.90
Purchase #5	$110.72	11.672%	$123.6432	$123.64	$123.65	$123.60
Purchase #6	$187.41	10.523%	$207.1312	$207.13	$207.15	$207.10
Purchase #7	$27.51	6.422%	$29.2767	$29.28	$29.30	$29.30
7 purchase totals =	$899.67		$994.0211	$994.02	$994.05	$994.00