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	$123.35	3.763%	$127.9917	$127.99	$128.00	$128.00
Purchase #2	$120.73	8.847%	$131.411	$131.41	$131.40	$131.40
Purchase #3	$42.81	7.587%	$46.058	$46.06	$46.05	$46.10
Purchase #4	$218.71	10.770%	$242.2651	$242.27	$242.25	$242.30
Purchase #5	$62.82	6.152%	$66.6847	$66.68	$66.70	$66.70
Purchase #6	$80.97	11.237%	$90.0686	$90.07	$90.05	$90.10
Purchase #7	$102.32	12.804%	$115.4211	$115.42	$115.40	$115.40
7 purchase totals =	$751.71		$819.9002	$819.90	$819.85	$820.00