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	$80.97	10.564%	$89.5237	$89.52	$89.50	$89.50
Purchase #2	$249.82	10.459%	$275.9487	$275.95	$275.95	$275.90
Purchase #3	$190.56	12.556%	$214.4867	$214.49	$214.50	$214.50
Purchase #4	$69.59	7.526%	$74.8273	$74.83	$74.85	$74.80
Purchase #5	$240.66	10.811%	$266.6778	$266.68	$266.70	$266.70
Purchase #6	$26.43	5.115%	$27.7819	$27.78	$27.80	$27.80
Purchase #7	$57.86	5.381%	$60.9734	$60.97	$60.95	$61.00
7 purchase totals =	$915.89		$1,010.2195	$1,010.22	$1,010.25	$1,010.20