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	$208.99	4.500%	$218.3946	$218.39	$218.40	$218.40
Purchase #2	$81.34	9.511%	$89.0762	$89.08	$89.10	$89.10
Purchase #3	$243.30	8.126%	$263.0706	$263.07	$263.05	$263.10
Purchase #4	$99.52	6.281%	$105.7709	$105.77	$105.75	$105.80
Purchase #5	$39.26	4.472%	$41.0157	$41.02	$41.00	$41.00
Purchase #6	$20.28	5.816%	$21.4595	$21.46	$21.45	$21.50
Purchase #7	$248.50	12.448%	$279.4333	$279.43	$279.45	$279.40
7 purchase totals =	$941.19		$1,018.2208	$1,018.22	$1,018.20	$1,018.30