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	$45.28	11.259%	$50.3781	$50.38	$50.40	$50.40
Purchase #2	$102.38	6.360%	$108.8914	$108.89	$108.90	$108.90
Purchase #3	$170.98	5.294%	$180.0317	$180.03	$180.05	$180.00
Purchase #4	$201.32	10.414%	$222.2855	$222.29	$222.30	$222.30
Purchase #5	$218.91	5.475%	$230.8953	$230.90	$230.90	$230.90
Purchase #6	$80.32	10.247%	$88.5504	$88.55	$88.55	$88.60
Purchase #7	$191.37	6.783%	$204.3506	$204.35	$204.35	$204.40
7 purchase totals =	$1,010.56		$1,085.3830	$1,085.39	$1,085.45	$1,085.50