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	$18.49	12.685%	$20.8355	$20.84	$20.85	$20.80
Purchase #2	$224.71	4.350%	$234.4849	$234.48	$234.50	$234.50
Purchase #3	$197.51	13.234%	$223.6485	$223.65	$223.65	$223.60
Purchase #4	$188.28	11.135%	$209.245	$209.25	$209.25	$209.20
Purchase #5	$39.31	7.835%	$42.3899	$42.39	$42.40	$42.40
Purchase #6	$188.65	10.490%	$208.4394	$208.44	$208.45	$208.40
Purchase #7	$92.79	13.754%	$105.5523	$105.55	$105.55	$105.60
7 purchase totals =	$949.74		$1,044.5955	$1,044.60	$1,044.65	$1,044.50