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	$43.50	13.449%	$49.3503	$49.35	$49.35	$49.40
Purchase #2	$114.78	7.404%	$123.2783	$123.28	$123.30	$123.30
Purchase #3	$74.41	10.837%	$82.4738	$82.47	$82.45	$82.50
Purchase #4	$134.69	12.865%	$152.0179	$152.02	$152.00	$152.00
Purchase #5	$135.34	12.676%	$152.4957	$152.50	$152.50	$152.50
Purchase #6	$138.92	10.196%	$153.0843	$153.08	$153.10	$153.10
Purchase #7	$62.29	9.276%	$68.068	$68.07	$68.05	$68.10
7 purchase totals =	$703.93		$780.7683	$780.77	$780.75	$780.90