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	$155.63	13.281%	$176.2992	$176.30	$176.30	$176.30
Purchase #2	$121.88	4.450%	$127.3037	$127.30	$127.30	$127.30
Purchase #3	$13.69	8.499%	$14.8535	$14.85	$14.85	$14.90
Purchase #4	$13.87	4.584%	$14.5058	$14.51	$14.50	$14.50
Purchase #5	$72.37	8.278%	$78.3608	$78.36	$78.35	$78.40
Purchase #6	$133.35	13.566%	$151.4403	$151.44	$151.45	$151.40
Purchase #7	$113.75	3.111%	$117.2888	$117.29	$117.30	$117.30
7 purchase totals =	$624.54		$680.0521	$680.05	$680.05	$680.10