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	$52.47	10.212%	$57.8282	$57.83	$57.85	$57.80
Purchase #2	$36.85	8.481%	$39.9752	$39.98	$40.00	$40.00
Purchase #3	$10.83	5.406%	$11.4155	$11.42	$11.40	$11.40
Purchase #4	$169.37	8.185%	$183.2329	$183.23	$183.25	$183.20
Purchase #5	$170.34	7.685%	$183.4306	$183.43	$183.45	$183.40
Purchase #6	$57.33	7.867%	$61.8402	$61.84	$61.85	$61.80
Purchase #7	$247.86	6.868%	$264.883	$264.88	$264.90	$264.90
7 purchase totals =	$745.05		$802.6056	$802.61	$802.70	$802.50