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	$140.44	9.261%	$153.4461	$153.45	$153.45	$153.40
Purchase #2	$127.58	10.145%	$140.523	$140.52	$140.50	$140.50
Purchase #3	$57.55	8.355%	$62.3583	$62.36	$62.35	$62.40
Purchase #4	$204.47	5.156%	$215.0125	$215.01	$215.00	$215.00
Purchase #5	$205.81	3.274%	$212.5482	$212.55	$212.55	$212.50
Purchase #6	$89.76	10.553%	$99.2324	$99.23	$99.25	$99.20
Purchase #7	$17.72	8.476%	$19.2219	$19.22	$19.20	$19.20
7 purchase totals =	$843.33		$902.3424	$902.34	$902.30	$902.20