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	$84.72	13.841%	$96.4461	$96.45	$96.45	$96.40
Purchase #2	$165.43	12.707%	$186.4512	$186.45	$186.45	$186.50
Purchase #3	$158.96	10.610%	$175.8257	$175.83	$175.85	$175.80
Purchase #4	$87.53	6.857%	$93.5319	$93.53	$93.55	$93.50
Purchase #5	$126.49	6.583%	$134.8168	$134.82	$134.80	$134.80
Purchase #6	$103.85	13.398%	$117.7638	$117.76	$117.75	$117.80
Purchase #7	$69.48	12.870%	$78.4221	$78.42	$78.40	$78.40
7 purchase totals =	$796.46		$883.2576	$883.26	$883.25	$883.20