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	$225.45	6.628%	$240.3928	$240.39	$240.40	$240.40
Purchase #2	$85.88	5.853%	$90.9066	$90.91	$90.90	$90.90
Purchase #3	$17.98	4.716%	$18.8279	$18.83	$18.85	$18.80
Purchase #4	$71.67	10.402%	$79.1251	$79.13	$79.15	$79.10
Purchase #5	$172.61	8.709%	$187.6426	$187.64	$187.65	$187.60
Purchase #6	$137.99	13.561%	$156.7028	$156.70	$156.70	$156.70
Purchase #7	$108.61	10.359%	$119.8609	$119.86	$119.85	$119.90
7 purchase totals =	$820.19		$893.4587	$893.46	$893.50	$893.40