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	$10.75	10.230%	$11.8497	$11.85	$11.85	$11.80
Purchase #2	$159.40	4.283%	$166.2271	$166.23	$166.25	$166.20
Purchase #3	$89.90	4.661%	$94.0902	$94.09	$94.10	$94.10
Purchase #4	$121.41	8.256%	$131.4336	$131.43	$131.45	$131.40
Purchase #5	$149.83	11.520%	$167.0904	$167.09	$167.10	$167.10
Purchase #6	$81.97	3.745%	$85.0398	$85.04	$85.05	$85.00
Purchase #7	$101.51	10.552%	$112.2213	$112.22	$112.20	$112.20
7 purchase totals =	$714.77		$767.9521	$767.95	$768.00	$767.80