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	$99.25	12.736%	$111.8905	$111.89	$111.90	$111.90
Purchase #2	$93.65	11.321%	$104.2521	$104.25	$104.25	$104.30
Purchase #3	$190.99	13.783%	$217.3142	$217.31	$217.30	$217.30
Purchase #4	$6.40	6.646%	$6.8253	$6.83	$6.85	$6.80
Purchase #5	$81.92	11.779%	$91.5694	$91.57	$91.55	$91.60
Purchase #6	$118.91	7.412%	$127.7236	$127.72	$127.70	$127.70
Purchase #7	$176.34	10.341%	$194.5753	$194.58	$194.60	$194.60
7 purchase totals =	$767.46		$854.1504	$854.15	$854.15	$854.20