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	$47.50	13.122%	$53.733	$53.73	$53.75	$53.70
Purchase #2	$112.59	5.108%	$118.3411	$118.34	$118.35	$118.30
Purchase #3	$28.46	5.335%	$29.9783	$29.98	$30.00	$30.00
Purchase #4	$178.81	6.514%	$190.4577	$190.46	$190.45	$190.50
Purchase #5	$241.36	5.684%	$255.0789	$255.08	$255.10	$255.10
Purchase #6	$45.82	9.863%	$50.3392	$50.34	$50.35	$50.30
Purchase #7	$42.90	13.176%	$48.5525	$48.55	$48.55	$48.60
7 purchase totals =	$697.44		$746.4807	$746.48	$746.55	$746.50