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	$179.95	5.282%	$189.455	$189.46	$189.45	$189.50
Purchase #2	$169.38	10.233%	$186.7127	$186.71	$186.70	$186.70
Purchase #3	$217.25	7.420%	$233.37	$233.37	$233.35	$233.40
Purchase #4	$97.72	9.256%	$106.765	$106.77	$106.75	$106.80
Purchase #5	$246.37	3.690%	$255.4611	$255.46	$255.45	$255.50
Purchase #6	$31.83	3.724%	$33.0153	$33.02	$33.00	$33.00
Purchase #7	$122.33	7.350%	$131.3213	$131.32	$131.30	$131.30
7 purchase totals =	$1,064.83		$1,136.1004	$1,136.11	$1,136.00	$1,136.20