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	$52.64	4.170%	$54.8351	$54.84	$54.85	$54.80
Purchase #2	$132.41	9.382%	$144.8327	$144.83	$144.85	$144.80
Purchase #3	$57.74	3.186%	$59.5796	$59.58	$59.60	$59.60
Purchase #4	$237.42	5.856%	$251.3233	$251.32	$251.30	$251.30
Purchase #5	$78.25	9.512%	$85.6931	$85.69	$85.70	$85.70
Purchase #6	$220.52	13.802%	$250.9562	$250.96	$250.95	$251.00
Purchase #7	$49.34	8.237%	$53.4041	$53.40	$53.40	$53.40
7 purchase totals =	$828.32		$900.6241	$900.62	$900.65	$900.60