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	$54.59	3.328%	$56.4068	$56.41	$56.40	$56.40
Purchase #2	$113.36	13.386%	$128.5344	$128.53	$128.55	$128.50
Purchase #3	$238.28	9.538%	$261.0071	$261.01	$261.00	$261.00
Purchase #4	$72.46	9.678%	$79.4727	$79.47	$79.45	$79.50
Purchase #5	$184.30	4.846%	$193.2312	$193.23	$193.25	$193.20
Purchase #6	$19.57	5.186%	$20.5849	$20.58	$20.60	$20.60
Purchase #7	$105.74	5.461%	$111.5145	$111.51	$111.50	$111.50
7 purchase totals =	$788.30		$850.7516	$850.74	$850.75	$850.70