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	$76.28	3.603%	$79.0284	$79.03	$79.05	$79.00
Purchase #2	$132.79	11.868%	$148.5495	$148.55	$148.55	$148.50
Purchase #3	$98.61	13.209%	$111.6354	$111.64	$111.65	$111.60
Purchase #4	$33.59	11.657%	$37.5056	$37.51	$37.50	$37.50
Purchase #5	$226.42	10.440%	$250.0582	$250.06	$250.05	$250.10
Purchase #6	$168.62	5.538%	$177.9582	$177.96	$177.95	$178.00
Purchase #7	$80.94	8.111%	$87.505	$87.51	$87.50	$87.50
7 purchase totals =	$817.25		$892.2403	$892.26	$892.25	$892.20