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	$49.67	10.439%	$54.8551	$54.86	$54.85	$54.90
Purchase #2	$115.77	10.286%	$127.6781	$127.68	$127.70	$127.70
Purchase #3	$96.72	9.325%	$105.7391	$105.74	$105.75	$105.70
Purchase #4	$47.73	7.528%	$51.3231	$51.32	$51.30	$51.30
Purchase #5	$85.33	6.397%	$90.7886	$90.79	$90.80	$90.80
Purchase #6	$72.61	10.372%	$80.1411	$80.14	$80.15	$80.10
Purchase #7	$102.56	12.396%	$115.2733	$115.27	$115.25	$115.30
7 purchase totals =	$570.39		$625.7984	$625.80	$625.80	$625.80