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	$49.36	11.429%	$55.0014	$55.00	$55.00	$55.00
Purchase #2	$117.72	8.587%	$127.8286	$127.83	$127.85	$127.80
Purchase #3	$140.92	12.746%	$158.8817	$158.88	$158.90	$158.90
Purchase #4	$79.68	13.203%	$90.2002	$90.20	$90.20	$90.20
Purchase #5	$156.59	9.388%	$171.2907	$171.29	$171.30	$171.30
Purchase #6	$167.40	11.361%	$186.4183	$186.42	$186.40	$186.40
Purchase #7	$59.60	5.182%	$62.6885	$62.69	$62.70	$62.70
7 purchase totals =	$771.27		$852.3094	$852.31	$852.35	$852.30