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	$76.40	11.361%	$85.0798	$85.08	$85.10	$85.10
Purchase #2	$14.53	3.404%	$15.0246	$15.02	$15.00	$15.00
Purchase #3	$39.74	5.709%	$42.0088	$42.01	$42.00	$42.00
Purchase #4	$116.53	9.734%	$127.873	$127.87	$127.85	$127.90
Purchase #5	$105.72	5.857%	$111.912	$111.91	$111.90	$111.90
Purchase #6	$249.44	10.420%	$275.4316	$275.43	$275.45	$275.40
Purchase #7	$134.95	8.117%	$145.9039	$145.90	$145.90	$145.90
7 purchase totals =	$737.31		$803.2337	$803.22	$803.20	$803.20