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	$43.53	4.142%	$45.333	$45.33	$45.35	$45.30
Purchase #2	$145.69	10.270%	$160.6524	$160.65	$160.65	$160.70
Purchase #3	$29.49	6.581%	$31.4307	$31.43	$31.45	$31.40
Purchase #4	$134.52	9.669%	$147.5267	$147.53	$147.55	$147.50
Purchase #5	$81.47	4.461%	$85.1044	$85.10	$85.10	$85.10
Purchase #6	$104.68	7.577%	$112.6116	$112.61	$112.60	$112.60
Purchase #7	$16.68	5.118%	$17.5337	$17.53	$17.55	$17.50
7 purchase totals =	$556.06		$600.1925	$600.18	$600.25	$600.10