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	$19.81	10.269%	$21.8443	$21.84	$21.85	$21.80
Purchase #2	$141.77	4.779%	$148.5452	$148.55	$148.55	$148.50
Purchase #3	$65.69	8.308%	$71.1475	$71.15	$71.15	$71.10
Purchase #4	$127.88	13.643%	$145.3267	$145.33	$145.35	$145.30
Purchase #5	$239.33	13.747%	$272.2307	$272.23	$272.25	$272.20
Purchase #6	$198.39	3.529%	$205.3912	$205.39	$205.40	$205.40
Purchase #7	$207.50	3.740%	$215.2605	$215.26	$215.25	$215.30
7 purchase totals =	$1,000.37		$1,079.7461	$1,079.75	$1,079.80	$1,079.60