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	$50.51	3.447%	$52.2511	$52.25	$52.25	$52.30
Purchase #2	$125.64	11.136%	$139.6313	$139.63	$139.65	$139.60
Purchase #3	$138.97	10.439%	$153.4771	$153.48	$153.50	$153.50
Purchase #4	$117.31	10.211%	$129.2885	$129.29	$129.30	$129.30
Purchase #5	$83.67	8.405%	$90.7025	$90.70	$90.70	$90.70
Purchase #6	$161.85	6.323%	$172.0838	$172.08	$172.10	$172.10
Purchase #7	$73.48	4.603%	$76.8623	$76.86	$76.85	$76.90
7 purchase totals =	$751.43		$814.2966	$814.29	$814.35	$814.40