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	$210.30	10.812%	$233.0376	$233.04	$233.05	$233.00
Purchase #2	$89.32	10.187%	$98.419	$98.42	$98.40	$98.40
Purchase #3	$59.46	3.259%	$61.3978	$61.40	$61.40	$61.40
Purchase #4	$222.96	12.116%	$249.9738	$249.97	$249.95	$250.00
Purchase #5	$242.81	4.729%	$254.2925	$254.29	$254.30	$254.30
Purchase #6	$202.37	13.204%	$229.0909	$229.09	$229.10	$229.10
Purchase #7	$92.85	13.863%	$105.7218	$105.72	$105.70	$105.70
7 purchase totals =	$1,120.07		$1,231.9334	$1,231.93	$1,231.90	$1,231.90