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	$88.33	7.404%	$94.87	$94.87	$94.85	$94.90
Purchase #2	$111.72	8.839%	$121.5949	$121.59	$121.60	$121.60
Purchase #3	$78.39	3.740%	$81.3218	$81.32	$81.30	$81.30
Purchase #4	$158.59	5.561%	$167.4092	$167.41	$167.40	$167.40
Purchase #5	$37.54	10.235%	$41.3822	$41.38	$41.40	$41.40
Purchase #6	$97.92	13.509%	$111.148	$111.15	$111.15	$111.10
Purchase #7	$28.91	10.553%	$31.9609	$31.96	$31.95	$32.00
7 purchase totals =	$601.40		$649.6870	$649.68	$649.65	$649.70