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	$49.28	9.656%	$54.0385	$54.04	$54.05	$54.00
Purchase #2	$151.71	9.620%	$166.3045	$166.30	$166.30	$166.30
Purchase #3	$172.31	13.400%	$195.3995	$195.40	$195.40	$195.40
Purchase #4	$39.81	11.157%	$44.2516	$44.25	$44.25	$44.30
Purchase #5	$133.51	9.815%	$146.614	$146.61	$146.60	$146.60
Purchase #6	$50.93	12.707%	$57.4017	$57.40	$57.40	$57.40
Purchase #7	$80.97	11.620%	$90.3787	$90.38	$90.40	$90.40
7 purchase totals =	$678.52		$754.3885	$754.38	$754.40	$754.40