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	$244.39	7.728%	$263.2765	$263.28	$263.30	$263.30
Purchase #2	$59.40	9.149%	$64.8345	$64.83	$64.85	$64.80
Purchase #3	$124.89	7.769%	$134.5927	$134.59	$134.60	$134.60
Purchase #4	$160.25	13.831%	$182.4142	$182.41	$182.40	$182.40
Purchase #5	$33.79	12.511%	$38.0175	$38.02	$38.00	$38.00
Purchase #6	$169.43	6.580%	$180.5785	$180.58	$180.60	$180.60
Purchase #7	$208.25	13.670%	$236.7178	$236.72	$236.70	$236.70
7 purchase totals =	$1,000.40		$1,100.4317	$1,100.43	$1,100.45	$1,100.40