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	$99.56	8.496%	$108.0186	$108.02	$108.00	$108.00
Purchase #2	$101.37	8.374%	$109.8587	$109.86	$109.85	$109.90
Purchase #3	$212.53	9.441%	$232.595	$232.60	$232.60	$232.60
Purchase #4	$15.55	10.121%	$17.1238	$17.12	$17.10	$17.10
Purchase #5	$144.94	4.799%	$151.8957	$151.90	$151.90	$151.90
Purchase #6	$103.49	8.599%	$112.3891	$112.39	$112.40	$112.40
Purchase #7	$106.25	4.870%	$111.4244	$111.42	$111.40	$111.40
7 purchase totals =	$783.69		$843.3053	$843.31	$843.25	$843.30