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	$137.54	13.630%	$156.2867	$156.29	$156.30	$156.30
Purchase #2	$136.63	12.237%	$153.3494	$153.35	$153.35	$153.30
Purchase #3	$248.30	11.726%	$277.4157	$277.42	$277.40	$277.40
Purchase #4	$54.38	10.747%	$60.2242	$60.22	$60.20	$60.20
Purchase #5	$158.77	3.812%	$164.8223	$164.82	$164.80	$164.80
Purchase #6	$10.48	7.427%	$11.2583	$11.26	$11.25	$11.30
Purchase #7	$227.59	4.827%	$238.5758	$238.58	$238.60	$238.60
7 purchase totals =	$973.69		$1,061.9324	$1,061.94	$1,061.90	$1,061.90