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	$109.90	4.449%	$114.7895	$114.79	$114.80	$114.80
Purchase #2	$234.45	12.657%	$264.1243	$264.12	$264.10	$264.10
Purchase #3	$90.39	10.590%	$99.9623	$99.96	$99.95	$100.00
Purchase #4	$42.53	13.746%	$48.3762	$48.38	$48.40	$48.40
Purchase #5	$145.42	9.728%	$159.5665	$159.57	$159.55	$159.60
Purchase #6	$95.72	10.153%	$105.4385	$105.44	$105.45	$105.40
Purchase #7	$34.48	10.450%	$38.0832	$38.08	$38.10	$38.10
7 purchase totals =	$752.89		$830.3405	$830.34	$830.35	$830.40