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	$59.87	9.244%	$65.4044	$65.40	$65.40	$65.40
Purchase #2	$39.94	10.719%	$44.2212	$44.22	$44.20	$44.20
Purchase #3	$124.35	10.407%	$137.2911	$137.29	$137.30	$137.30
Purchase #4	$70.70	13.463%	$80.2183	$80.22	$80.20	$80.20
Purchase #5	$89.42	12.751%	$100.8219	$100.82	$100.80	$100.80
Purchase #6	$19.80	3.486%	$20.4902	$20.49	$20.50	$20.50
Purchase #7	$187.36	11.522%	$208.9476	$208.95	$208.95	$208.90
7 purchase totals =	$591.44		$657.3947	$657.39	$657.35	$657.30