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	$163.77	10.418%	$180.8316	$180.83	$180.85	$180.80
Purchase #2	$206.32	11.146%	$229.3164	$229.32	$229.30	$229.30
Purchase #3	$50.93	13.599%	$57.856	$57.86	$57.85	$57.90
Purchase #4	$112.56	11.465%	$125.465	$125.47	$125.45	$125.50
Purchase #5	$51.99	5.252%	$54.7205	$54.72	$54.70	$54.70
Purchase #6	$84.30	12.339%	$94.7018	$94.70	$94.70	$94.70
Purchase #7	$33.83	10.491%	$37.3791	$37.38	$37.40	$37.40
7 purchase totals =	$703.70		$780.2704	$780.28	$780.25	$780.30