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	$81.40	10.362%	$89.8347	$89.83	$89.85	$89.80
Purchase #2	$212.42	9.856%	$233.3561	$233.36	$233.35	$233.40
Purchase #3	$44.30	12.204%	$49.7064	$49.71	$49.70	$49.70
Purchase #4	$21.42	13.630%	$24.3395	$24.34	$24.35	$24.30
Purchase #5	$51.38	12.441%	$57.7722	$57.77	$57.75	$57.80
Purchase #6	$152.91	9.502%	$167.4395	$167.44	$167.45	$167.40
Purchase #7	$134.40	13.375%	$152.376	$152.38	$152.40	$152.40
7 purchase totals =	$698.23		$774.8244	$774.83	$774.85	$774.80