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	$100.76	10.561%	$111.4013	$111.40	$111.40	$111.40
Purchase #2	$118.39	7.725%	$127.5356	$127.54	$127.55	$127.50
Purchase #3	$145.62	11.643%	$162.5745	$162.57	$162.55	$162.60
Purchase #4	$58.77	13.859%	$66.9149	$66.91	$66.90	$66.90
Purchase #5	$217.52	11.159%	$241.7931	$241.79	$241.80	$241.80
Purchase #6	$248.53	11.583%	$277.3172	$277.32	$277.30	$277.30
Purchase #7	$127.47	11.411%	$142.0156	$142.02	$142.00	$142.00
7 purchase totals =	$1,017.06		$1,129.5522	$1,129.55	$1,129.50	$1,129.50