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	$142.31	9.688%	$156.097	$156.10	$156.10	$156.10
Purchase #2	$193.30	6.641%	$206.1371	$206.14	$206.15	$206.10
Purchase #3	$160.60	3.780%	$166.6707	$166.67	$166.65	$166.70
Purchase #4	$177.72	10.337%	$196.0909	$196.09	$196.10	$196.10
Purchase #5	$37.42	12.833%	$42.2221	$42.22	$42.20	$42.20
Purchase #6	$131.76	5.167%	$138.568	$138.57	$138.55	$138.60
Purchase #7	$69.39	12.576%	$78.1165	$78.12	$78.10	$78.10
7 purchase totals =	$912.50		$983.9023	$983.91	$983.85	$983.90