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	$166.93	13.776%	$189.9263	$189.93	$189.95	$189.90
Purchase #2	$99.60	9.785%	$109.3459	$109.35	$109.35	$109.30
Purchase #3	$158.55	13.154%	$179.4057	$179.41	$179.40	$179.40
Purchase #4	$11.44	7.412%	$12.2879	$12.29	$12.30	$12.30
Purchase #5	$185.42	7.609%	$199.5286	$199.53	$199.55	$199.50
Purchase #6	$135.95	11.247%	$151.2403	$151.24	$151.25	$151.20
Purchase #7	$160.26	9.583%	$175.6177	$175.62	$175.60	$175.60
7 purchase totals =	$918.15		$1,017.3524	$1,017.37	$1,017.40	$1,017.20