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	$57.77	3.322%	$59.6891	$59.69	$59.70	$59.70
Purchase #2	$40.50	11.628%	$45.2093	$45.21	$45.20	$45.20
Purchase #3	$250.26	10.129%	$275.6088	$275.61	$275.60	$275.60
Purchase #4	$156.38	10.824%	$173.3066	$173.31	$173.30	$173.30
Purchase #5	$10.25	11.625%	$11.4416	$11.44	$11.45	$11.40
Purchase #6	$166.72	5.203%	$175.3944	$175.39	$175.40	$175.40
Purchase #7	$151.83	10.571%	$167.8799	$167.88	$167.90	$167.90
7 purchase totals =	$833.71		$908.5297	$908.53	$908.55	$908.50