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	$243.27	5.279%	$256.1122	$256.11	$256.10	$256.10
Purchase #2	$24.86	10.725%	$27.5262	$27.53	$27.55	$27.50
Purchase #3	$36.29	10.254%	$40.0112	$40.01	$40.00	$40.00
Purchase #4	$236.80	11.678%	$264.4535	$264.45	$264.45	$264.50
Purchase #5	$30.79	4.136%	$32.0635	$32.06	$32.05	$32.10
Purchase #6	$187.45	12.203%	$210.3245	$210.32	$210.30	$210.30
Purchase #7	$16.96	6.832%	$18.1187	$18.12	$18.10	$18.10
7 purchase totals =	$776.42		$848.6098	$848.60	$848.55	$848.60