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	$118.54	4.343%	$123.6882	$123.69	$123.70	$123.70
Purchase #2	$208.46	12.689%	$234.9115	$234.91	$234.90	$234.90
Purchase #3	$108.45	4.577%	$113.4138	$113.41	$113.40	$113.40
Purchase #4	$91.32	12.852%	$103.0564	$103.06	$103.05	$103.10
Purchase #5	$49.92	7.741%	$53.7843	$53.78	$53.80	$53.80
Purchase #6	$13.50	9.667%	$14.805	$14.81	$14.80	$14.80
Purchase #7	$156.74	8.201%	$169.5942	$169.59	$169.60	$169.60
7 purchase totals =	$746.93		$813.2534	$813.25	$813.25	$813.30