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	$57.77	3.730%	$59.9248	$59.92	$59.90	$59.90
Purchase #2	$75.95	6.585%	$80.9513	$80.95	$80.95	$81.00
Purchase #3	$54.39	11.612%	$60.7058	$60.71	$60.70	$60.70
Purchase #4	$70.85	10.659%	$78.4019	$78.40	$78.40	$78.40
Purchase #5	$122.94	5.150%	$129.2714	$129.27	$129.25	$129.30
Purchase #6	$93.64	8.213%	$101.3307	$101.33	$101.35	$101.30
Purchase #7	$165.69	9.525%	$181.472	$181.47	$181.45	$181.50
7 purchase totals =	$641.23		$692.0579	$692.05	$692.00	$692.10