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	$60.31	13.548%	$68.4808	$68.48	$68.50	$68.50
Purchase #2	$39.45	6.201%	$41.8963	$41.90	$41.90	$41.90
Purchase #3	$83.29	9.348%	$91.0759	$91.08	$91.10	$91.10
Purchase #4	$151.75	11.211%	$168.7627	$168.76	$168.75	$168.80
Purchase #5	$46.56	7.643%	$50.1186	$50.12	$50.10	$50.10
Purchase #6	$73.76	12.118%	$82.6982	$82.70	$82.70	$82.70
Purchase #7	$116.91	6.150%	$124.1	$124.10	$124.10	$124.10
7 purchase totals =	$572.03		$627.1325	$627.14	$627.15	$627.20