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	$151.77	13.561%	$172.3515	$172.35	$172.35	$172.40
Purchase #2	$39.33	13.187%	$44.5164	$44.52	$44.50	$44.50
Purchase #3	$73.29	9.724%	$80.4167	$80.42	$80.40	$80.40
Purchase #4	$233.91	11.570%	$260.9734	$260.97	$260.95	$261.00
Purchase #5	$29.85	13.292%	$33.8177	$33.82	$33.80	$33.80
Purchase #6	$114.48	11.687%	$127.8593	$127.86	$127.85	$127.90
Purchase #7	$161.95	7.595%	$174.2501	$174.25	$174.25	$174.30
7 purchase totals =	$804.58		$894.1851	$894.19	$894.10	$894.30