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	$19.77	5.438%	$20.8451	$20.85	$20.85	$20.80
Purchase #2	$153.85	4.485%	$160.7502	$160.75	$160.75	$160.80
Purchase #3	$85.31	5.201%	$89.747	$89.75	$89.75	$89.70
Purchase #4	$90.94	13.354%	$103.0841	$103.08	$103.10	$103.10
Purchase #5	$243.94	5.152%	$256.5078	$256.51	$256.50	$256.50
Purchase #6	$72.42	8.699%	$78.7198	$78.72	$78.70	$78.70
Purchase #7	$105.71	8.161%	$114.337	$114.34	$114.35	$114.30
7 purchase totals =	$771.94		$823.9910	$824.00	$824.00	$823.90