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	$54.50	9.116%	$59.4682	$59.47	$59.45	$59.50
Purchase #2	$83.50	5.861%	$88.3939	$88.39	$88.40	$88.40
Purchase #3	$178.43	13.872%	$203.1818	$203.18	$203.20	$203.20
Purchase #4	$199.60	3.743%	$207.071	$207.07	$207.05	$207.10
Purchase #5	$194.40	13.823%	$221.2719	$221.27	$221.25	$221.30
Purchase #6	$116.88	11.728%	$130.5877	$130.59	$130.60	$130.60
Purchase #7	$86.56	4.685%	$90.6153	$90.62	$90.60	$90.60
7 purchase totals =	$913.87		$1,000.5898	$1,000.59	$1,000.55	$1,000.70