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	$9.68	12.710%	$10.9103	$10.91	$10.90	$10.90
Purchase #2	$202.43	13.312%	$229.3775	$229.38	$229.40	$229.40
Purchase #3	$226.69	7.129%	$242.8507	$242.85	$242.85	$242.90
Purchase #4	$221.59	5.387%	$233.5271	$233.53	$233.55	$233.50
Purchase #5	$145.38	7.217%	$155.8721	$155.87	$155.85	$155.90
Purchase #6	$151.77	8.408%	$164.5308	$164.53	$164.55	$164.50
Purchase #7	$127.60	9.361%	$139.5446	$139.54	$139.55	$139.50
7 purchase totals =	$1,085.14		$1,176.6131	$1,176.61	$1,176.65	$1,176.60