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	$71.80	10.667%	$79.4589	$79.46	$79.45	$79.50
Purchase #2	$10.88	5.140%	$11.4392	$11.44	$11.45	$11.40
Purchase #3	$63.68	12.551%	$71.6725	$71.67	$71.65	$71.70
Purchase #4	$103.54	4.556%	$108.2573	$108.26	$108.25	$108.30
Purchase #5	$168.78	5.556%	$178.1574	$178.16	$178.15	$178.20
Purchase #6	$109.88	4.447%	$114.7664	$114.77	$114.75	$114.80
Purchase #7	$99.39	6.192%	$105.5442	$105.54	$105.55	$105.50
7 purchase totals =	$627.95		$669.2959	$669.30	$669.25	$669.40