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	$226.60	12.650%	$255.2649	$255.26	$255.25	$255.30
Purchase #2	$138.52	4.309%	$144.4888	$144.49	$144.50	$144.50
Purchase #3	$19.59	9.834%	$21.5165	$21.52	$21.50	$21.50
Purchase #4	$71.69	12.358%	$80.5495	$80.55	$80.55	$80.50
Purchase #5	$168.91	10.183%	$186.1101	$186.11	$186.10	$186.10
Purchase #6	$15.25	5.825%	$16.1383	$16.14	$16.15	$16.10
Purchase #7	$160.80	11.481%	$179.2614	$179.26	$179.25	$179.30
7 purchase totals =	$801.36		$883.3295	$883.33	$883.30	$883.30