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	$226.76	11.579%	$253.0165	$253.02	$253.00	$253.00
Purchase #2	$36.40	6.742%	$38.8541	$38.85	$38.85	$38.90
Purchase #3	$136.56	5.789%	$144.4655	$144.47	$144.45	$144.50
Purchase #4	$90.57	11.568%	$101.0471	$101.05	$101.05	$101.00
Purchase #5	$20.52	7.823%	$22.1253	$22.13	$22.15	$22.10
Purchase #6	$99.64	13.295%	$112.8871	$112.89	$112.90	$112.90
Purchase #7	$82.57	9.823%	$90.6809	$90.68	$90.70	$90.70
7 purchase totals =	$693.02		$763.0765	$763.09	$763.10	$763.10