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	$19.50	10.225%	$21.4939	$21.49	$21.50	$21.50
Purchase #2	$208.39	7.679%	$224.3923	$224.39	$224.40	$224.40
Purchase #3	$243.25	5.190%	$255.8747	$255.87	$255.85	$255.90
Purchase #4	$123.33	3.719%	$127.9166	$127.92	$127.90	$127.90
Purchase #5	$181.44	10.832%	$201.0936	$201.09	$201.10	$201.10
Purchase #6	$70.88	7.659%	$76.3087	$76.31	$76.30	$76.30
Purchase #7	$100.84	9.407%	$110.326	$110.33	$110.35	$110.30
7 purchase totals =	$947.63		$1,017.4058	$1,017.40	$1,017.40	$1,017.40