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	$19.85	4.608%	$20.7647	$20.76	$20.75	$20.80
Purchase #2	$242.59	7.318%	$260.3427	$260.34	$260.35	$260.30
Purchase #3	$70.92	10.569%	$78.4155	$78.42	$78.40	$78.40
Purchase #4	$169.43	9.751%	$185.9511	$185.95	$185.95	$186.00
Purchase #5	$147.45	10.209%	$162.5032	$162.50	$162.50	$162.50
Purchase #6	$203.74	11.670%	$227.5165	$227.52	$227.50	$227.50
Purchase #7	$16.59	9.172%	$18.1116	$18.11	$18.10	$18.10
7 purchase totals =	$870.57		$953.6053	$953.60	$953.55	$953.60