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	$40.28	7.280%	$43.2124	$43.21	$43.20	$43.20
Purchase #2	$52.93	13.849%	$60.2603	$60.26	$60.25	$60.30
Purchase #3	$112.55	13.320%	$127.5417	$127.54	$127.55	$127.50
Purchase #4	$210.60	5.825%	$222.8675	$222.87	$222.85	$222.90
Purchase #5	$63.51	6.205%	$67.4508	$67.45	$67.45	$67.50
Purchase #6	$221.26	8.175%	$239.348	$239.35	$239.35	$239.30
Purchase #7	$49.31	13.444%	$55.9392	$55.94	$55.95	$55.90
7 purchase totals =	$750.44		$816.6199	$816.62	$816.60	$816.60