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	$121.86	4.231%	$127.0159	$127.02	$127.00	$127.00
Purchase #2	$109.55	5.541%	$115.6202	$115.62	$115.60	$115.60
Purchase #3	$232.32	12.484%	$261.3228	$261.32	$261.30	$261.30
Purchase #4	$81.25	4.711%	$85.0777	$85.08	$85.10	$85.10
Purchase #5	$113.37	8.568%	$123.0835	$123.08	$123.10	$123.10
Purchase #6	$134.73	13.727%	$153.2244	$153.22	$153.20	$153.20
Purchase #7	$154.82	12.521%	$174.205	$174.21	$174.20	$174.20
7 purchase totals =	$947.90		$1,039.5495	$1,039.55	$1,039.50	$1,039.50