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	$89.49	12.242%	$100.4454	$100.45	$100.45	$100.40
Purchase #2	$81.27	8.848%	$88.4608	$88.46	$88.45	$88.50
Purchase #3	$28.55	10.667%	$31.5954	$31.60	$31.60	$31.60
Purchase #4	$28.84	5.725%	$30.4911	$30.49	$30.50	$30.50
Purchase #5	$19.28	9.582%	$21.1274	$21.13	$21.15	$21.10
Purchase #6	$101.66	6.707%	$108.4783	$108.48	$108.50	$108.50
Purchase #7	$117.92	11.666%	$131.6765	$131.68	$131.70	$131.70
7 purchase totals =	$467.01		$512.2749	$512.29	$512.35	$512.30