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	$18.31	13.461%	$20.7747	$20.77	$20.75	$20.80
Purchase #2	$72.31	9.307%	$79.0399	$79.04	$79.05	$79.00
Purchase #3	$153.68	10.839%	$170.3374	$170.34	$170.35	$170.30
Purchase #4	$191.84	12.662%	$216.1308	$216.13	$216.15	$216.10
Purchase #5	$233.61	4.387%	$243.8585	$243.86	$243.85	$243.90
Purchase #6	$13.46	6.747%	$14.3681	$14.37	$14.35	$14.40
Purchase #7	$83.54	8.480%	$90.6242	$90.62	$90.60	$90.60
7 purchase totals =	$766.75		$835.1336	$835.13	$835.10	$835.10