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	$9.32	11.711%	$10.4115	$10.41	$10.40	$10.40
Purchase #2	$37.77	11.758%	$42.211	$42.21	$42.20	$42.20
Purchase #3	$17.78	13.398%	$20.1622	$20.16	$20.15	$20.20
Purchase #4	$103.72	13.534%	$117.7575	$117.76	$117.75	$117.80
Purchase #5	$141.67	8.394%	$153.5618	$153.56	$153.55	$153.60
Purchase #6	$37.54	7.161%	$40.2282	$40.23	$40.25	$40.20
Purchase #7	$40.65	6.561%	$43.317	$43.32	$43.30	$43.30
7 purchase totals =	$388.45		$427.6492	$427.65	$427.60	$427.70