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	$125.95	10.696%	$139.4216	$139.42	$139.40	$139.40
Purchase #2	$242.27	12.594%	$272.7815	$272.78	$272.80	$272.80
Purchase #3	$149.58	8.556%	$162.3781	$162.38	$162.40	$162.40
Purchase #4	$178.52	7.864%	$192.5588	$192.56	$192.55	$192.60
Purchase #5	$31.95	9.787%	$35.0769	$35.08	$35.10	$35.10
Purchase #6	$100.71	4.689%	$105.4323	$105.43	$105.45	$105.40
Purchase #7	$212.44	10.692%	$235.1541	$235.15	$235.15	$235.20
7 purchase totals =	$1,041.42		$1,142.8033	$1,142.80	$1,142.85	$1,142.90