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	$177.59	4.842%	$186.1889	$186.19	$186.20	$186.20
Purchase #2	$61.60	7.760%	$66.3802	$66.38	$66.40	$66.40
Purchase #3	$143.73	10.657%	$159.0473	$159.05	$159.05	$159.00
Purchase #4	$168.90	10.263%	$186.2342	$186.23	$186.25	$186.20
Purchase #5	$117.31	12.429%	$131.8905	$131.89	$131.90	$131.90
Purchase #6	$179.75	10.652%	$198.897	$198.90	$198.90	$198.90
Purchase #7	$150.31	13.591%	$170.7386	$170.74	$170.75	$170.70
7 purchase totals =	$999.19		$1,099.3767	$1,099.38	$1,099.45	$1,099.30