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	$105.89	8.757%	$115.1628	$115.16	$115.15	$115.20
Purchase #2	$227.27	13.376%	$257.6696	$257.67	$257.65	$257.70
Purchase #3	$38.45	11.383%	$42.8268	$42.83	$42.85	$42.80
Purchase #4	$49.75	11.848%	$55.6444	$55.64	$55.65	$55.60
Purchase #5	$225.87	12.500%	$254.1038	$254.10	$254.10	$254.10
Purchase #6	$90.45	4.737%	$94.7346	$94.73	$94.75	$94.70
Purchase #7	$96.74	4.793%	$101.3767	$101.38	$101.40	$101.40
7 purchase totals =	$834.42		$921.5187	$921.51	$921.55	$921.50