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	$249.67	11.398%	$278.1274	$278.13	$278.15	$278.10
Purchase #2	$72.67	8.107%	$78.5614	$78.56	$78.55	$78.60
Purchase #3	$72.59	12.256%	$81.4866	$81.49	$81.50	$81.50
Purchase #4	$140.70	5.789%	$148.8451	$148.85	$148.85	$148.80
Purchase #5	$139.91	3.583%	$144.923	$144.92	$144.90	$144.90
Purchase #6	$30.52	5.173%	$32.0988	$32.10	$32.10	$32.10
Purchase #7	$56.50	10.415%	$62.3845	$62.38	$62.40	$62.40
7 purchase totals =	$762.56		$826.4268	$826.43	$826.45	$826.40