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	$91.47	12.717%	$103.1022	$103.10	$103.10	$103.10
Purchase #2	$241.79	10.745%	$267.7703	$267.77	$267.75	$267.80
Purchase #3	$166.62	13.811%	$189.6319	$189.63	$189.65	$189.60
Purchase #4	$88.51	6.505%	$94.2676	$94.27	$94.25	$94.30
Purchase #5	$153.88	8.320%	$166.6828	$166.68	$166.70	$166.70
Purchase #6	$154.78	8.846%	$168.4718	$168.47	$168.45	$168.50
Purchase #7	$9.40	11.301%	$10.4623	$10.46	$10.45	$10.50
7 purchase totals =	$906.45		$1,000.3889	$1,000.38	$1,000.35	$1,000.50