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	$242.56	11.385%	$270.1755	$270.18	$270.20	$270.20
Purchase #2	$133.58	6.694%	$142.5218	$142.52	$142.50	$142.50
Purchase #3	$24.61	12.766%	$27.7517	$27.75	$27.75	$27.80
Purchase #4	$80.28	10.182%	$88.4541	$88.45	$88.45	$88.50
Purchase #5	$165.54	8.740%	$180.0082	$180.01	$180.00	$180.00
Purchase #6	$50.37	9.204%	$55.0061	$55.01	$55.00	$55.00
Purchase #7	$250.82	12.304%	$281.6809	$281.68	$281.70	$281.70
7 purchase totals =	$947.76		$1,045.5983	$1,045.60	$1,045.60	$1,045.70