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	$217.36	13.820%	$247.3992	$247.40	$247.40	$247.40
Purchase #2	$17.72	13.196%	$20.0583	$20.06	$20.05	$20.10
Purchase #3	$165.67	7.858%	$178.6883	$178.69	$178.70	$178.70
Purchase #4	$29.85	5.296%	$31.4309	$31.43	$31.45	$31.40
Purchase #5	$80.71	6.721%	$86.1345	$86.13	$86.15	$86.10
Purchase #6	$227.40	3.296%	$234.8951	$234.90	$234.90	$234.90
Purchase #7	$184.91	3.440%	$191.2709	$191.27	$191.25	$191.30
7 purchase totals =	$923.62		$989.8772	$989.88	$989.90	$989.90