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	$44.85	11.159%	$49.8548	$49.85	$49.85	$49.90
Purchase #2	$72.58	6.133%	$77.0313	$77.03	$77.05	$77.00
Purchase #3	$165.59	10.624%	$183.1823	$183.18	$183.20	$183.20
Purchase #4	$109.26	5.169%	$114.9076	$114.91	$114.90	$114.90
Purchase #5	$113.86	11.692%	$127.1725	$127.17	$127.15	$127.20
Purchase #6	$39.44	5.441%	$41.5859	$41.59	$41.60	$41.60
Purchase #7	$90.38	10.671%	$100.0244	$100.02	$100.00	$100.00
7 purchase totals =	$635.96		$693.7588	$693.75	$693.75	$693.80