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	$18.79	7.866%	$20.268	$20.27	$20.25	$20.30
Purchase #2	$81.47	13.626%	$92.5711	$92.57	$92.55	$92.60
Purchase #3	$130.95	9.365%	$143.2135	$143.21	$143.20	$143.20
Purchase #4	$63.38	3.580%	$65.649	$65.65	$65.65	$65.60
Purchase #5	$47.43	8.339%	$51.3852	$51.39	$51.40	$51.40
Purchase #6	$131.52	9.399%	$143.8816	$143.88	$143.90	$143.90
Purchase #7	$99.70	5.494%	$105.1775	$105.18	$105.20	$105.20
7 purchase totals =	$573.24		$622.1459	$622.15	$622.15	$622.20