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	$78.51	5.736%	$83.0133	$83.01	$83.00	$83.00
Purchase #2	$140.98	12.684%	$158.8619	$158.86	$158.85	$158.90
Purchase #3	$123.28	13.394%	$139.7921	$139.79	$139.80	$139.80
Purchase #4	$113.45	12.185%	$127.2739	$127.27	$127.25	$127.30
Purchase #5	$164.29	8.654%	$178.5077	$178.51	$178.50	$178.50
Purchase #6	$46.42	5.690%	$49.0613	$49.06	$49.05	$49.10
Purchase #7	$235.70	6.373%	$250.7212	$250.72	$250.70	$250.70
7 purchase totals =	$902.63		$987.2314	$987.22	$987.15	$987.30