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	$54.85	4.503%	$57.3199	$57.32	$57.30	$57.30
Purchase #2	$46.73	10.431%	$51.6044	$51.60	$51.60	$51.60
Purchase #3	$232.94	9.618%	$255.3442	$255.34	$255.35	$255.30
Purchase #4	$232.38	6.271%	$246.9525	$246.95	$246.95	$247.00
Purchase #5	$132.63	7.470%	$142.5375	$142.54	$142.55	$142.50
Purchase #6	$93.94	12.602%	$105.7783	$105.78	$105.80	$105.80
Purchase #7	$74.69	6.114%	$79.2565	$79.26	$79.25	$79.30
7 purchase totals =	$868.16		$938.7933	$938.79	$938.80	$938.80