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	$68.82	9.767%	$75.5416	$75.54	$75.55	$75.50
Purchase #2	$95.66	5.534%	$100.9538	$100.95	$100.95	$101.00
Purchase #3	$221.94	8.210%	$240.1613	$240.16	$240.15	$240.20
Purchase #4	$105.27	6.243%	$111.842	$111.84	$111.85	$111.80
Purchase #5	$41.39	12.318%	$46.4884	$46.49	$46.50	$46.50
Purchase #6	$111.64	5.488%	$117.7668	$117.77	$117.75	$117.80
Purchase #7	$139.30	7.868%	$150.2601	$150.26	$150.25	$150.30
7 purchase totals =	$784.02		$843.0140	$843.01	$843.00	$843.10