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	$161.60	3.842%	$167.8087	$167.81	$167.80	$167.80
Purchase #2	$230.52	13.541%	$261.7347	$261.73	$261.75	$261.70
Purchase #3	$88.94	13.186%	$100.6676	$100.67	$100.65	$100.70
Purchase #4	$60.72	7.517%	$65.2843	$65.28	$65.30	$65.30
Purchase #5	$46.91	10.500%	$51.8356	$51.84	$51.85	$51.80
Purchase #6	$50.36	11.587%	$56.1952	$56.20	$56.20	$56.20
Purchase #7	$127.61	11.181%	$141.8781	$141.88	$141.90	$141.90
7 purchase totals =	$766.66		$845.4042	$845.41	$845.45	$845.40