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	$217.88	6.449%	$231.9311	$231.93	$231.95	$231.90
Purchase #2	$64.98	7.860%	$70.0874	$70.09	$70.10	$70.10
Purchase #3	$16.56	13.178%	$18.7423	$18.74	$18.75	$18.70
Purchase #4	$156.86	10.261%	$172.9554	$172.96	$172.95	$173.00
Purchase #5	$87.64	3.122%	$90.3761	$90.38	$90.40	$90.40
Purchase #6	$147.88	5.847%	$156.5265	$156.53	$156.55	$156.50
Purchase #7	$191.40	3.589%	$198.2693	$198.27	$198.25	$198.30
7 purchase totals =	$883.20		$938.8881	$938.90	$938.95	$938.90