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	$160.92	11.753%	$179.8329	$179.83	$179.85	$179.80
Purchase #2	$104.59	3.635%	$108.3918	$108.39	$108.40	$108.40
Purchase #3	$37.71	13.636%	$42.8521	$42.85	$42.85	$42.90
Purchase #4	$189.92	13.420%	$215.4073	$215.41	$215.40	$215.40
Purchase #5	$160.82	7.651%	$173.1243	$173.12	$173.10	$173.10
Purchase #6	$103.76	8.334%	$112.4074	$112.41	$112.40	$112.40
Purchase #7	$97.45	13.531%	$110.636	$110.64	$110.65	$110.60
7 purchase totals =	$855.17		$942.6518	$942.65	$942.65	$942.60