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	$167.63	6.633%	$178.7489	$178.75	$178.75	$178.70
Purchase #2	$139.90	7.486%	$150.3729	$150.37	$150.35	$150.40
Purchase #3	$233.68	13.483%	$265.1871	$265.19	$265.20	$265.20
Purchase #4	$145.91	11.821%	$163.158	$163.16	$163.15	$163.20
Purchase #5	$172.41	13.704%	$196.0371	$196.04	$196.05	$196.00
Purchase #6	$49.73	10.757%	$55.0795	$55.08	$55.10	$55.10
Purchase #7	$118.99	10.322%	$131.2721	$131.27	$131.25	$131.30
7 purchase totals =	$1,028.25		$1,139.8556	$1,139.86	$1,139.85	$1,139.90