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	$122.56	9.654%	$134.3919	$134.39	$134.40	$134.40
Purchase #2	$38.35	4.866%	$40.2161	$40.22	$40.20	$40.20
Purchase #3	$249.30	11.370%	$277.6454	$277.65	$277.65	$277.60
Purchase #4	$163.59	5.394%	$172.414	$172.41	$172.40	$172.40
Purchase #5	$146.62	6.474%	$156.1122	$156.11	$156.10	$156.10
Purchase #6	$18.35	13.225%	$20.7768	$20.78	$20.80	$20.80
Purchase #7	$37.61	12.309%	$42.2394	$42.24	$42.25	$42.20
7 purchase totals =	$776.38		$843.7958	$843.80	$843.80	$843.70