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	$168.35	6.158%	$178.717	$178.72	$178.70	$178.70
Purchase #2	$112.52	9.620%	$123.3444	$123.34	$123.35	$123.30
Purchase #3	$172.80	12.505%	$194.4086	$194.41	$194.40	$194.40
Purchase #4	$129.29	7.214%	$138.617	$138.62	$138.60	$138.60
Purchase #5	$69.75	12.563%	$78.5127	$78.51	$78.50	$78.50
Purchase #6	$53.50	3.851%	$55.5603	$55.56	$55.55	$55.60
Purchase #7	$192.59	8.456%	$208.8754	$208.88	$208.90	$208.90
7 purchase totals =	$898.80		$978.0354	$978.04	$978.00	$978.00