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	$19.56	7.675%	$21.0612	$21.06	$21.05	$21.10
Purchase #2	$117.75	9.689%	$129.1588	$129.16	$129.15	$129.20
Purchase #3	$223.87	12.293%	$251.3903	$251.39	$251.40	$251.40
Purchase #4	$132.70	7.654%	$142.8569	$142.86	$142.85	$142.90
Purchase #5	$72.96	12.102%	$81.7896	$81.79	$81.80	$81.80
Purchase #6	$179.27	6.575%	$191.057	$191.06	$191.05	$191.10
Purchase #7	$85.93	5.849%	$90.956	$90.96	$90.95	$91.00
7 purchase totals =	$832.04		$908.2698	$908.28	$908.25	$908.50