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	$167.86	11.767%	$187.6121	$187.61	$187.60	$187.60
Purchase #2	$123.35	7.383%	$132.4569	$132.46	$132.45	$132.50
Purchase #3	$173.37	9.307%	$189.5055	$189.51	$189.50	$189.50
Purchase #4	$50.80	6.180%	$53.9394	$53.94	$53.95	$53.90
Purchase #5	$72.84	3.846%	$75.6414	$75.64	$75.65	$75.60
Purchase #6	$160.58	7.380%	$172.4308	$172.43	$172.45	$172.40
Purchase #7	$61.65	6.772%	$65.8249	$65.82	$65.80	$65.80
7 purchase totals =	$810.45		$877.4110	$877.41	$877.40	$877.30